MORGAN STANLEY SENIOR FUNDING, INC. 1585 Broadway New York, New York 10036

EXHIBIT 10.2

March 24, 2007

Beckman Coulter, Inc.

P.O. Box 3100

4300 N. Harbor Blvd.

Fullerton, CA ###-###-####

Attention: Chief Financial Officer

Beckman Coulter, Inc.

$1,650,000,000 Interim Term Loan Facility

Commitment Letter

Ladies and Gentlemen:

Beckman Coulter, Inc., a Delaware corporation (the “Borrower” or “you”) has advised Morgan Stanley Senior Funding, Inc. (“Morgan Stanley”) and Citigroup Global Markets Inc. (“CGMI”, and, together with Citigroup (as defined below) and Morgan Stanley, “us”) regarding your proposed acquisition (the “Acquisition”) of the stock of Biosite Incorporated, a Delaware corporation (the “Target”). As we understand the transaction, pursuant to an Agreement and Plan of Merger (including all annexes and exhibits thereto, the “Acquisition Agreement”) to be entered into with the Target and the Purchaser (as defined therein) and a tender offer conducted in accordance with the terms of the Acquisition Agreement (the “Tender Offer”) followed by a merger with the Target (the “Merger”), you will purchase all of the outstanding capital stock of the Target. The consideration for the Acquisition will be comprised of all cash. The Acquisition effected by the Tender Offer and the Merger, the financings contemplated by the foregoing and the payment of fees and expenses associated therewith are collectively referred to as the “Transaction”. For purposes of this Commitment Letter, “Citigroup” means CGMI, Citibank, N.A., Citicorp USA, Inc., Citicorp North America, Inc. and/or any of their affiliates as may be appropriate to consummate the transactions contemplated herein.

More specifically, you have informed us that the Borrower intends to arrange for a commitment of up to a $1,650,000,000 interim term loan facility (the “Interim Term Loan Facility”, also herein referred to as the “Interim Facility”). We understand that borrowings under the Interim Facility (if any) will be used to fund the Transaction.

In connection with the Transaction (a) (i) Morgan Stanley is pleased to advise you of its commitment to provide, on a several (and not joint) basis, or to cause one or more of its affiliates to provide, 50.0% of the Interim Facility and (ii) Citigroup is pleased to advise you of its commitment to provide, on a several (and not joint) basis, or to cause one or more of its affiliates to provide, 50.0% of the Interim Facility subject to and on the terms and conditions set forth herein and in the summary of and conditions attached as Annex I (the “Term Sheet” which, together with this letter, are herein collectively referred to as the “Commitment Letter”) and (b) Morgan Stanley and

Citigroup (collectively, the “Arrangers”) shall use commercially reasonable efforts to arrange a syndicate of Lenders (as defined in the Term Sheet) to participate in the Interim Facility.

You agree that Citigroup shall act as sole and exclusive administrative agent (in such capacity, the “Administrative Agent”), and, together with Morgan Stanley, co-lead arranger and joint bookrunner in respect of the Interim Facility (Morgan Stanley to be “on the left”). It is understood that the Arrangers shall be permitted to designate one or more Lenders as agents or co-agents, as the case may be, with respect to the Interim Facility in their sole discretion, but no other agents, co-agents or arrangers will be appointed, no other titles may be given, and no other compensation (other than as expressly set forth in the Term Sheet or in the Fee Letter described below) will be paid without the Arrangers’ prior written consent; provided, however, that you may, within 10 days of the announcement of the Acquisition, appoint additional co-managers for up to 20% of the commitment of the Interim Term Loan Facility. Fees payable to the syndicate of Lenders shall be payable from the amounts payable by the Borrower pursuant to the fee letter (the “Fee Letter”) among the parties hereto and executed simultaneously herewith.

Each of Morgan Stanley and Citigroup (the “Initial Lenders”) reserve the right, prior to or after execution of the definitive credit documentation for the Interim Facility, to syndicate all or part of its commitment for the Interim Facility to one or more lending institutions reasonably acceptable to you that will become parties to the appropriate definitive credit documentation pursuant to a syndication in respect of the Interim Facility to be managed by the Arrangers, and the commitment of the Initial Lenders hereunder in respect of the Interim Facility shall be reduced as and when commitments are received from the other financial institutions in respect of the Interim Facility. The Arrangers may commence syndication efforts promptly after the execution of this letter by you and you agree actively to assist the Arrangers in achieving a syndication in respect of the Interim Facility that is satisfactory to the Arrangers. Such syndication will be accomplished by a variety of means, including direct contact during the syndication for the Interim Facility between senior financial management and advisors of the Borrower and the proposed syndicate members for the Interim Facility (such members, the “Lenders”). To assist the Arrangers in their syndication efforts, you hereby agree (i) to provide and cause your advisors to provide the Arrangers and the other relevant syndicate members upon request with all information reasonably deemed necessary by the Arrangers to complete syndication, including but not limited to information prepared by you and your advisors or on your behalf relating to the transactions contemplated hereby, (ii) to assist the Arrangers upon request in the preparation of an information memorandum (the “Information Memorandum”) to be used in connection with the syndication of the Interim Facility, (iii) to use your commercially reasonable efforts to ensure that the syndication efforts of the Arrangers benefit materially from your existing lending relationships and the existing lending relationships of the Target, (iv) to make available your senior financial officers and representatives and, to use your commercially reasonable efforts to make available Target’s senior financial officers and representatives, in each case from time to time to attend and make presentations regarding the business and prospects of the Borrower and Target at a meeting or meetings of prospective Lenders and (v) to use commercially reasonable efforts to obtain a “Corporate Family Rating” from Moody’s Investors Service, Inc. (“Moody’s”), and a “Corporate Rating” from Standard & Poor’s Ratings Services, a division of The McGraw-Hill Companies, Inc. (“S&P”). The Arrangers will manage all aspects of any syndication in consultation with you, including decisions as to the selection of institutions to be approached and when they will be approached, when their commitments will be accepted, which institutions will participate, the allocation of the commitments among the Lenders and the amount and distribution of fees among the Lenders. You will also afford the Arrangers a period of at least 20 consecutive days following the launch of the general syndication of the Interim Facility and immediately prior to the Closing Date of the Interim Facility to syndicate the Interim Facility. In addition, you agree that, without the

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consent of the Arrangers (such consent not to be unreasonably withheld or delayed), until the earliest of completion of the primary syndication of the Interim Facility, the termination of the commitment of Morgan Stanley and Citigroup and 90 days after the commencement of the primary syndication, no financing (other than the Interim Facility and the Permanent Financing (as defined in the Term Sheet)) for you or any of your subsidiaries shall be syndicated, privately placed or publicly offered in the United States or Europe to the extent that such financing would have an adverse effect on the syndication of the Interim Facility; provided, however, that the foregoing shall not limit your ability or that of your subsidiaries to (i) issue commercial paper or other short-term debt programs currently in place, (ii) amend, waive, modify, renew or refinance your existing revolving credit facility (the “Existing Credit Facility”), or other financings to fund operations or for working capital, or borrow thereunder, (iii) refinance any indebtedness outstanding on the date hereof, (iv) incur purchase money indebtedness for the acquisition of assets used in the business, (v) incur indebtedness in connection with the exercise of the “Top-Up Option” under the Acquisition Agreement, or (vi) incur other limited indebtedness to be agreed upon.

In addition, all commitments, undertakings and agreements hereunder are subject to (i) the absence of a “Company Material Adverse Effect” (as defined in the Acquisition Agreement), (ii) (a) the accuracy and completeness in all material respects of all representations that you make to us (subject to clause (x) below), (b) your compliance in all material respects with the terms of this Commitment Letter and (c) your compliance in all material respects with the terms of the Fee Letter and (iii) the negotiation, execution and delivery of definitive documentation with respect to the Interim Facility (the “Loan Documentation”), which shall, in each case, be consistent with the Term Sheet and the Existing Credit Facility as further set forth therein (provided that, notwithstanding anything in this Commitment Letter, the Fee Letter, the Loan Documentation or any other letter agreement or other undertaking concerning the financing of the Transaction to the contrary, (x) the only representations relating to the Borrower, the Target, their respective subsidiaries and their businesses the making of which shall be a condition to availability of the Interim Facility on the Closing Date shall be (A) such of the representations made by the Target in the Acquisition Agreement, as are material to the interests of the Lenders, but only to the extent that you have the right to terminate your obligations under the Acquisition Agreement as a result of a breach of such representations in the Acquisition Agreement and (B) the Specified Representations (as defined below) and (y) the terms of the Loan Documentation shall be in a form such that they do not impair availability of the Interim Facility on the Closing Date or the Delayed Draw Funding Date (as defined in the Term Sheet) if the conditions set forth herein and in the Term Sheet are satisfied. Those matters that are not covered by or made clear under the provisions of this Commitment Letter are subject to the approval and agreement of the Agent and you; provided that such approvals and agreements shall be in a manner that is consistent with the Term Sheet. For purposes hereof, “Specified Representations” means the representations and warranties set forth in the Term Sheet relating to corporate power and authority, due authorization, execution and delivery of the Loan Documentation, no conflicts with material contractual restrictions, the enforceability of the Loan Documentation, Federal Reserve margin regulations and the Investment Company Act.

To induce Morgan Stanley and Citigroup to issue this letter and to continue with their due diligence efforts, you hereby agree that all reasonable out-of-pocket fees and expenses (including the reasonable fees and expenses of Skadden, Arps, Slate, Meagher & Flom, LLP, counsel to the Arrangers) of Morgan Stanley, Citigroup and their affiliates arising in connection with this letter (and its due diligence and syndication efforts in connection herewith) and in connection with the Interim Facility shall be for your account, payable whether or not the Transaction is consummated. In addition, you hereby agree to pay when and as due the fees described in the Fee Letter.

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You further agree to indemnify and hold harmless each of the Administrative Agent, the Arrangers, the Lenders (including, in any event, Morgan Stanley and Citigroup), each other agent under the Interim Facility and each director, officer, employee and affiliate thereof, and each other person controlling any of the foregoing within the meaning of either Section 15 of the Securities Act of 1933, as amended, or Section 20 of the Securities Exchange Act of 1934, as amended (each an “Indemnified Person”) from and against any and all actions, suits, proceedings (including any investigations or inquiries), claims, losses, damages, liabilities or expenses of any kind or nature whatsoever which may be incurred by or asserted against or involve any such Indemnified Person as a result of or arising out of or in any way related to or resulting from this Commitment Letter, the Fee Letter, the Engagement Letter, the Transaction, the extension or syndication of the Interim Facility contemplated by this Commitment Letter, or in any way arising from any use or intended use of this letter or the proceeds of the Interim Facility contemplated by this Commitment Letter, and you agree to reimburse each Indemnified Person upon demand for any reasonable legal or other out-of-pocket expenses incurred in connection with investigating, defending or preparing to defend any such action, suit, proceeding (including any inquiry or investigation) or claim (whether or not Morgan Stanley, Citigroup or any such other Indemnified Person is a party to any action or proceeding out of which any such expenses arise) (collectively, an “Action”); provided, however, that you shall not have to indemnify any Indemnified Person against any loss, claim, damage, expense or liability to the extent finally determined by a court of competent jurisdiction to have resulted from the gross negligence, willful misconduct or material breach of this Commitment Letter of such Indemnified Person. In the case of an investigation, litigation or other proceeding to which the indemnity in this paragraph applies, such indemnity shall be effective whether or not such investigation, litigation or proceeding is brought by the you, any of your directors, security holders or creditors, an Indemnified Person or any other person or an Indemnified Person is otherwise a party thereto and whether or not the transactions contemplated hereby are consummated. The Borrower shall have no obligation to indemnify and hold harmless any Indemnified Party to the extent that any claim, loss, cost, or expense arises from a failure by such Indemnified Party to comply with laws, regulations, rules or orders that may apply to its business or a failure by such Indemnified Party to possess the capacity to participate in the transactions contemplated by this letter or to take all actions necessary to authorize its participation in such transactions. The provisions of this paragraph shall be superseded by the applicable provisions contained in the Loan Documentation.

You will not, without the prior written consent of the affected Indemnified Person(s), settle, compromise, consent to the entry of any judgment in or otherwise seek to terminate any Action in respect of which indemnification may be sought hereunder unless such settlement, compromise, consent or termination includes a full and unconditional release of such Indemnified Person(s) from any liabilities arising out of such Action.

The provisions of the immediately preceding three paragraphs shall survive any termination of this Commitment Letter.

Each of Morgan Stanley and Citigroup reserve the right to employ the services of its affiliates in providing services contemplated by this Commitment Letter and to allocate, in whole or in part, to such affiliates certain fees payable to Morgan Stanley and Citigroup in such manner as each of Morgan Stanley, Citigroup and such affiliates may agree in their sole discretion. You acknowledge that Morgan Stanley and Citigroup may, on a confidential basis, share with any of their affiliates, and such affiliates may share with Morgan Stanley and Citigroup, any information related to the Transaction, you, the Borrower, the Target, any of its subsidiaries or any of the matters contemplated hereby in connection with the Transaction.

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You hereby represent and warrant that, as to the Target and its subsidiaries, to the best of your knowledge, and, as to the Borrower and its subsidiaries, that (i) all information (other than the Projections referred to below, information of a general economic or general industry nature and information as to the Target (which has been derived from publicly available information and in respect of which no representation is made) that has been made available by you or will hereafter be made available by you in connection with the Transaction (the “Information”) to Morgan Stanley, Citigroup or any of their affiliates or representatives or to any Lender or any potential Lender when taken as a whole is, or in the case of Information made available after the date hereof, will be correct in all material respects and does not and will not, when furnished, contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements contained therein not misleading in light of the circumstances under which such statements were or are made (after giving effect to all supplements thereto) and (ii) all financial projections, if any, that have been or will be prepared by you and made available to Morgan Stanley, Citigroup or any of their affiliates or representatives or to any Lender or any potential Lender in connection with the Transaction (the “Projections”) have been or, in the case of Projections made available after the date hereof, will be prepared in good faith based upon assumptions believed by you to be reasonable (it being understood that such projections are subject to significant uncertainties and contingencies, many of which are beyond your control, and that no assurance can be given that any particular projections will be realized). You agree that you will promptly notify (and deliver copies to) Morgan Stanley and Citigroup of any changes in circumstances or any additional information that would be reasonably expected to call into question the Information or the continued reasonableness of any assumption underlying the Projections, and that you will supplement the Information and the Projections as necessary so that the representations, warranties and covenants set forth in this paragraph concerning the Information and the Projections remain complete and correct without regard to when such Information and Projections were made available. In issuing this commitment, Morgan Stanley and Citigroup are relying on the accuracy of the Information and on the reasonableness of the Projections as described above without independent verification thereof. The representations and covenants contained in this paragraph shall remain effective until the definitive Loan Documentation is executed and thereafter the disclosure representations contained herein shall be terminated and of no further force and effect.

You hereby acknowledge that the Arrangers will make available Information and Projections to the proposed syndicate of Lenders and that certain of the proposed Lenders may be “public-side” Lenders (i.e., Lenders that do not wish to receive material non-public information with respect to Borrower) (each, a “Public Lender”). You hereby agree that (a) you will use commercially reasonable efforts to identify that portion of the Information and Projections that may be distributed to the Public Lenders and include a reasonably detailed term sheet in such Information and that all of the foregoing that is to be made available to Public Lenders shall be clearly and conspicuously marked “PUBLIC”; (b) by marking materials “PUBLIC,” you shall be deemed to have authorized the Arrangers and the proposed Lenders to treat such materials as not containing any material non-public information with respect to the Borrower for purposes of United States federal and state securities laws, it being understood that certain of such materials may be subject to the confidentiality requirements of the definitive Loan Documentation; (c) all materials marked “PUBLIC” are permitted to be made available by means designated “Public Investor;” and (d) the Arrangers shall treat any materials that are not marked “PUBLIC” as being suitable only for dissemination by means not designated for “Public Lenders.”

You understand and acknowledge that Morgan Stanley, Citigroup and their respective affiliates may be providing debt financing, equity capital or other services (including, without limitation, financial advisory services) to other companies that may have interests which conflict with yours regarding the Transaction and otherwise. None of Morgan Stanley, Citigroup or

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their respective affiliates shall use confidential information obtained from you (or on your behalf) or the Target in connection with the performance by Morgan Stanley, Citigroup or their respective affiliates of services for other companies, and none of Morgan Stanley, Citigroup or their respective affiliates will furnish any such confidential information to other companies. You acknowledge that none of Morgan Stanley, Citigroup or their respective affiliates have any obligation to use, in connection with the Transaction or otherwise, or to furnish to you, confidential information obtained from other companies.

This Commitment Letter, the Term Sheet attached hereto and the Fee Letter (collectively referred to as the “Commitment Documents”) are delivered to you with the understanding that no Commitment Document, nor the substance hereof or thereof, shall be disclosed to any third party (including, without limitation, other lenders, arrangers, underwriters, placement agents, or advisors or any similar persons), without our prior written consent, except (i) to your officers, employees, agents, accountants, legal advisors and other agents and advisors (and then only on a confidential and need to know basis), (ii) to the Target and its officers, employees, agents, accountants, legal advisors and other agents and advisors (and then only on a confidential and need to know basis and excluding the Fee Letter (other than any “market” flex provisions contained therein)) and (iii) as required by law or any court, governmental agency, rating agency or stock exchange requirements (provided, that you agree to promptly inform us following any such permitted disclosure); provided that you may disclose the Commitment Letter and its contents in any public filing with the Securities and Exchange Commission or any applicable stock exchange or in any prospectus or offering memorandum; provided further, that the foregoing restrictions shall cease to apply (except in respect of the Fee Letter and the contents thereof) after the Loan Documentation shall have been executed and delivered by the parties thereto.

Neither we, nor our respective affiliates shall disclose to any person any Transaction Information (as defined below) without the prior written consent of the Borrower other than to those affiliates, officers, directors, employees and advisors and to actual or prospective Lenders who have agreed to maintain confidential such information or as required or requested by law or regulation (including any legal or regulatory proceeding or process). “Transaction Information” means any information about the Borrower and its subsidiaries or the Target and its subsidiaries not generally disclosed by the Borrower to, or known by, the public and that is not our possession or the possession of our respective affiliates prior to its being provided by or on behalf of the Borrower or becomes available to us or to our respective affiliates on a non-confidential basis, provided, in each case, that such information or source of such information is not known by us or our respective affiliates to be the subject of or bound by another confidentiality agreement with, or other legal or contractual obligation of confidentiality to, the Borrower or that is independently developed, discovered or arrived at by us or our respective affiliates.

We hereby notify you that, pursuant to the requirements of the USA Patriot Act, Title III of Pub. L. 107-56 (signed into law on October 26, 2001) (the “Patriot Act”), we are required to obtain, verify and record information that identifies you, which information includes names and addresses and other information that will allow us to identify you in accordance with the Patriot Act.

This Commitment Letter is delivered to you solely for your benefit and may not be relied upon by any other person or entity, and nothing in the Commitment Documents is intended to confer any rights upon, nor do the Commitment Documents create third-party beneficiary status in favor of, any other person or entity as to our commitments hereunder nor are the Commitment Documents assignable by you. You acknowledge that no fiduciary duty exists on our part owing to you or any other person or entity as a result of our delivery of the Commitment Documents and no

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other person shall have any other legal or equitable right, remedy or claim hereunder. This Commitment Letter may not be amended or modified, and no waiver will be effective, except by a writing duly executed by the parties hereto. None of Morgan Stanley, Citigroup nor any Lender shall be responsible or liable to you, the Target or any other person for consequential, special, indirect or punitive damages which may be alleged as a result of this letter.

The Commitment Documents constitute the entire understanding among the parties hereto with respect to the subject matter hereof and thereof and supersede any prior agreements, written or oral, with respect hereto or thereto. You irrevocably and unconditionally submit to the non-exclusive jurisdiction of any New York state or federal court (in each case) sitting in the County of New York over any suit, action or proceeding arising out of or relating to the Commitment Documents. Service of any process, summons, notice or document in any suit, action or proceeding may be made by registered mail addressed to you, Morgan Stanley or Citigroup, as appropriate, and you waive any claim that any such suit, action or proceeding has been brought in an inconvenient forum. A final judgment in any such suit, action or proceeding brought in any such court may be enforced in any other courts to whose jurisdiction you are or may be subject, by suit upon judgment. EACH COMMITMENT DOCUMENT SHALL BE DEEMED TO BE A CONTRACT MADE UNDER AND GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE INTERNAL LAWS OF THE STATE OF NEW YORK (INCLUDING, WITHOUT LIMITATION, FOR SUCH PURPOSE SECTIONS 5-1401 AND 5-1402 OF THE GENERAL OBLIGATIONS LAW OF THE STATE OF NEW YORK). EACH OF THE UNDERSIGNED PARTIES HEREBY KNOWINGLY, VOLUNTARILY AND INTENTIONALLY WAIVES ANY RIGHTS IT MAY HAVE TO A TRIAL BY JURY IN RESPECT OF ANY LITIGATION BASED HEREON, OR ARISING OUT OF OR IN CONNECTION WITH, ANY COMMITMENT DOCUMENT, AND ANY OTHER COURSE OF CONDUCT, COURSE OF DEALING, STATEMENTS (WHETHER ORAL OR WRITTEN) OR ACTIONS OF ANY OF THE UNDERSIGNED PARTIES IN CONNECTION WITH ANY COMMITMENT DOCUMENT. IN NO EVENT SHALL ANY PARTY TO THIS COMMITMENT LETTER BE LIABLE FOR CONSEQUENTIAL, SPECIAL, INDIRECT OR PUNITIVE DAMAGES IN CONNECTION WITH THE TRANSACTION OR ANY FINANCING TRANSACTION, OR WITH OUR DELIVERY OF THE COMMITMENT DOCUMENTS.

If the Commitment Documents are not accepted by you as provided in the immediately succeeding paragraph, you are to immediately return the Commitment Documents (and any copies thereof) to the undersigned. Please confirm that the foregoing is in accordance with your understanding by signing and returning to us an executed duplicate of the Commitment Documents. Each Commitment Document may be executed in any number of counterparts, and by the different parties hereto on separate counterparts, each of which counterpart shall be an original, but all of which shall together constitute one and the same instrument. Delivery of an executed counterpart of each Commitment Document by telecopier or other electronic communication shall be effective as delivery of a manually executed counterpart of such Commitment Document.

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This commitment will expire at 5:00 p.m. New York City time on April 2, 2007 unless it, the Fee Letter and the Engagement Letter are accepted by you prior to such time and, if accepted prior to such time, shall expire at the earliest of (i) consummation of the Transaction, (ii) 5:00 p.m. New York City time on August 31, 2007, if the closing of the Transaction shall not have occurred by such time and (iii) termination of the Acquisition Agreement. You may terminate this Commitment Letter at any time by written notice to the Arrangers.

Very truly yours,

MORGAN STANLEY SENIOR

FUNDING, INC.

By /s/ Kevin M. Sisson                        

Name: Kevin M. Sisson

Title: Managing Director

CITIGROUP GLOBAL MARKETS INC.

By /s/ J. Gregory Davis                            

Name: J. Gregory Davis

Title: Authorized Signatory

Agreed to and Accepted this 24th day of March, 2007

BECKMAN COULTER, INC.

By /s/ Arnold A. Pinkston                    

Name: Arnold A. Pinkston

Title: Senior Vice President, General Counsel and Secretary

ANNEX I

SUMMARY OF CERTAIN TERMS AND CONDITIONS*

$1,650,000,000 INTERIM FACILITY

I. The Parties

II. Description of Credit Facility

I-2

III. Terms Applicable to the Interim Facility

I-3

I-4

I-5

I-6

I-7

I-8

SCHEDULE 1

to Annex I

INTERIM FACILITY PRICING

I-9

ANNEX II

CONDITIONS PRECEDENT TO THE CLOSING DATE AND THE DELAYED DRAW FUNDING DATE

Except as otherwise set forth below, the occurrence of the Closing Date and the Delayed Draw Funding Date shall be subject to the satisfaction of each of the following conditions precedent:

indebtedness incurred in connection with the Top-Up Option, and (vii) other limited indebtedness to be agreed upon.