COMMERCIAL GUARANTY

Exhibit 10.8(i)

COMMERCIAL GUARANTY

References in the shaded area are for Lender’s use only and do not limit the applicability of this document to any particular loan or item. Any item above containing “***” has been omitted due to text length limitations.

AMOUNT OF GUARANTY. The principal amount of this Guaranty is Sixteen Million Five Hundred Thousand & 00/100 Dollars ($16,500,000.00).

CONTINUING GUARANTY. For good and valuable consideration, Advanced Digital Imaging Research, LLC (“Guarantor”) absolutely and unconditionally guarantees and promises to pay to California Bank & Trust (“Lender”) or its order, in legal tender of the United States of America, the Indebtedness (as that term is defined below) of IRIS International, Inc. (“Borrower”) to Lender on the terms and conditions set forth in this Guaranty. The obligations of Guarantor under this Guaranty are continuing.

MAXIMUM LIABILITY. The maximum liability of Guarantor under this Guaranty shall not exceed at any one time the sum of the principal amount of $16,500,000.00, plus all interest thereon, plus all of Lender’s costs, expenses, and attorneys’ fees incurred in connection with or relating to (A) the collection of the Indebtedness, (B) the collection and sale of any collateral for the Indebtedness or this Guaranty, or (C) the enforcement of this Guaranty. Attorneys’ fees include, without limitation, attorneys’ fees whether or not there is a lawsuit, and if there is a lawsuit, any fees and costs for trial and appeals.

The above limitation on liability is not a restriction on the amount of the Indebtedness of Borrower to Lender either in the aggregate or at any one time. If Lender presently holds one or more guaranties, or hereafter receives additional guaranties from Guarantor, Lender’s rights under all guaranties shall be cumulative. This Guaranty shall not (unless specifically provided below to the contrary) affect or invalidate any such other guaranties. Guarantor’s liability will be Guarantor’s aggregate liability under the terms of this Guaranty and any such other unterminated guaranties.

INDEBTEDNESS GUARANTEED. The Indebtedness guaranteed by this Guaranty includes any and all of Borrower’s indebtedness to Lender and is used in the most comprehensive sense and means and includes any and all of Borrower’s liabilities, obligations and debts to Lender, now existing or hereinafter incurred or created, including, without limitation, all loans, advances, interest, costs, debts, overdraft indebtedness, credit card indebtedness, lease obligations, other obligations, and liabilities of Borrower, or any of them, and any present or future judgments against Borrower, or any of them; and whether any such Indebtedness is voluntarily or involuntarily incurred, due or not due, absolute or contingent, liquidated or unliquidated, determined or undetermined; whether Borrower may be liable individually or jointly with others, or primarily or secondarily, or as guarantor or surety; whether recovery on the Indebtedness may be or may become barred or unenforceable against Borrower for any reason whatsoever; and whether the Indebtedness arises from transactions which may be voidable on account of infancy, insanity, ultra vires, or otherwise.

DURATION OF GUARANTY. This Guaranty will take effect when received by Lender without the necessity of any acceptance by Lender, or any notice to Guarantor or to Borrower, and will continue in full force until all Indebtedness incurred or contracted before receipt by Lender of any notice of revocation shall have been fully and finally paid and satisfied and all of Guarantor’s other obligations under this Guaranty shall have been performed in full. If Guarantor elects to revoke this Guaranty, Guarantor may only do so in writing. Guarantor’s written notice of revocation must be mailed to Lender, by certified mail, at Lender’s address listed above or such other place as Lender may designate in writing. Written revocation of this Guaranty will apply only to advances or new Indebtedness created after actual receipt by Lender of Guarantor’s written revocation. For this purpose and without limitation, the term “new Indebtedness” does not include Indebtedness which at the time of notice of revocation is contingent, unliquidated, undetermined or not due and which later becomes absolute, liquidated, determined or due. This Guaranty will continue to bind Guarantor for all Indebtedness incurred by Borrower or committed by Lender prior to receipt of Guarantor’s written notice of revocation, including any extensions, renewals, substitutions or modifications of the Indebtedness. All renewals, extensions, substitutions, and modifications of the Indebtedness granted after Guarantor’s revocation, are contemplated under this Guaranty and, specifically will not be considered to be new Indebtedness. This Guaranty shall bind Guarantor’s estate as to Indebtedness created both before and after Guarantor’s death or incapacity, regardless of Lender’s actual notice of Guarantor’s death. Subject to the foregoing, Guarantor’s executor or administrator or other legal representative may terminate this Guaranty in the same manner in which Guarantor might have terminated it and with the same effect. Release of any other guarantor or termination of any other guaranty of the Indebtedness shall not affect the liability of Guarantor under this Guaranty. A revocation Lender receives from any one or more Guarantors shall not affect the liability of any remaining Guarantors under this Guaranty. It is anticipated that fluctuations may occur in the aggregate amount of Indebtedness covered by this Guaranty, and Guarantor specifically acknowledges and agrees that reductions in the amount of Indebtedness, even to zero dollars ($0.00), prior to Guarantor’s written revocation of this Guaranty shall not constitute a termination of this Guaranty. This Guaranty is binding upon Guarantor and Guarantor’s heirs, successors and assigns so long as any of the guaranteed Indebtedness remains unpaid and even though the Indebtedness guaranteed may from time to time be zero dollars ($0.00).

GUARANTOR’S AUTHORIZATION TO LENDER. Guarantor authorizes Lender, either before or after any revocation hereof, without notice or demand and without lessening Guarantor’s liability under this Guaranty, from time to time: (A) prior to revocation as set forth above, to make one or more additional secured or unsecured loans to Borrower, to lease equipment or other goods to Borrower, or otherwise to extend additional credit to Borrower; (B) to alter, compromise, renew, extend, accelerate, or otherwise change one or more times the time for payment or other terms of the Indebtedness or any part of the Indebtedness, including increases and decreases of the rate of interest on the Indebtedness; extensions may be repeated and may be for longer than the original loan term; (C) to take and hold security for the payment of this Guaranty or the Indebtedness, and exchange, enforce, waive, subordinate, fail or decide not to perfect, and release any such security, with or without the substitution of new collateral; (D) to release, substitute, agree not to sue, or deal with any one or more of Borrower’s sureties, endorsers, or other guarantors on any terms or in any manner Lender may choose; (E) to determine how, when and what application of payments and credits shall be made on the Indebtedness (F) to apply such security and direct the order or manner of sale thereof, including without limitation, any nonjudicial sale permitted by the terms of the controlling security agreement or deed of trust, as Lender in its discretion may determine; (G) to sell, transfer, assign or grant participations in all or any part of the Indebtedness; and (H) to assign or transfer this Guaranty in whole or in part.

GUARANTOR’S REPRESENTATIONS AND WARRANTIES. Guarantor represents and warrants to Lender that (A) no representations or agreements of any kind have been made to Guarantor which would limit or qualify in any way the terms of this Guaranty; (B) this Guaranty is

executed at Borrower’s request and not at the request of Lender; (C) Guarantor has full power, right and authority to enter into this Guaranty; (D) the provisions of this Guaranty do not conflict with or result in a default under any agreement or other instrument binding upon Guarantor and do not result in a violation of any law, regulation, court decree or order applicable to Guarantor; (E) Guarantor has not and will not, without the prior written consent of Lender, sell, lease, assign, encumber, hypothecate, transfer, or otherwise dispose of all or substantially all of Guarantor’s assets, or any interest therein; (F) upon Lender’s request, Guarantor will provide to Lender financial and credit information in form acceptable to Lender, and all such financial information which currently has been, and all future financial information which will be provided to Lender is and will be true and correct in all material respects and fairly present Guarantor’s financial condition as of the dates the financial information is provided; (G) no material adverse change has occurred in Guarantor’s financial condition since the date of the most recent financial statements provided to Lender and no event has occurred which may materially adversely affect Guarantor’s financial condition; (H) no litigation, claim, investigation, administrative proceeding or similar action (including those for unpaid taxes) against Guarantor is pending or threatened; (I) Lender has made no representation to Guarantor as to the creditworthiness of Borrower; and (J) Guarantor has established adequate means of obtaining from Borrower on a continuing basis information regarding Borrower’s financial condition. Guarantor agrees to keep adequately informed from such means of any facts, events, or circumstances which might in any way affect Guarantor’s risks under this Guaranty, and Guarantor further agrees that, absent a request for information, Lender shall have no obligation to disclose to Guarantor any information or documents acquired by Lender in the course of its relationship with Borrower.

GUARANTOR’S WAIVERS. Except as prohibited by applicable law, Guarantor waives any right to require Lender to (A) make any presentment, protest, demand, or notice of any kind, including notice of change of any terms of repayment of the Indebtedness, default by Borrower or any other guarantor or surety, any action or nonaction taken by Borrower, Lender, or any other guarantor or surety of Borrower, or the creation of new or additional Indebtedness; (B) proceed against any person, including Borrower, before proceeding against Guarantor; (C) proceed against any collateral for the Indebtedness, including Borrower’s collateral, before proceeding against Guarantor; (D) apply any payments or proceeds received against the Indebtedness in any order; (E) give notice of the terms, time, and place of any sale of the collateral pursuant to the Uniform Commercial Code or any other law governing such sale; (F) disclose any information about the Indebtedness, the Borrower, the collateral, or any other guarantor or surety, or about any action or nonaction of Lender; or (G) pursue any remedy or course of action in Lender’s power whatsoever.

Guarantor also waives any and all rights or defenses arising by reason of (H) any disability or other defense of Borrower, any other guarantor or surety or any other person; (I) the cessation from any cause whatsoever, other than payment in full, of the Indebtedness; (J) the application of proceeds of the Indebtedness by Borrower for purposes other than the purposes understood and intended by Guarantor and Lender; (K) any act of omission or commission by Lender which directly or indirectly results in or contributes to the discharge of Borrower or any other guarantor or surety, or the Indebtedness, or the loss or release of any collateral by operation of law or otherwise; (L) any statute of limitations in any action under this Guaranty or on the Indebtedness; or (M) any modification or change in terms of the Indebtedness, whatsoever, including without limitation, the renewal, extension, acceleration, or other change in the time payment of the Indebtedness is due and any change in the interest rate, and including any such modification or change in terms after revocation of this Guaranty on Indebtedness incurred prior to such revocation.

Guarantor waives all rights and any defenses arising out of an election of remedies by Lender even though that the election of remedies, such as a non-judicial foreclosure with respect to security for a guaranteed obligation, has destroyed Guarantor’s rights of subrogation and reimbursement against Borrower by operation of Section 580d of the California Code of Civil Procedure or otherwise.

Guarantor waives all rights and defenses that Guarantor may have because Borrower’s obligation is secured by real property. This means among other things: (1) Lender may collect from Guarantor without first foreclosing on any real or personal property collateral pledged by Borrower. (2) If Lender forecloses on any real property collateral pledged by Borrower: (a) the amount of Borrower’s obligation may be reduced only by the price for which the collateral is sold at the foreclosure sale, even if the collateral is worth more than the sale price. (b) Lender may collect from Guarantor even if Lender, by forclosing on the real property collateral, has destroyed any right Guarantor may have to collect from Borrower. This is an unconditional and irrevocable waiver of any rights and defenses Guarantor may have because Borrower’s obligation is secured by real property. These rights and defenses include, but are not limited to, any rights and defenses based upon Section 580a, 580b, 580d, or 726 of the Code of Civil Procedure.

Guarantor understands and agrees that the foregoing waivers are unconditional and irrevocable waivers of substantive rights and defenses to which Guarantor might otherwise be entitled under state and federal law. Guarantor acknowledges that Guarantor has provided these waivers of rights and defenses with the intention that they be fully relied upon by Lender. Guarantor further understands and agrees that this Guaranty is a separate and independent contract between Guarantor and Lender, given for full and ample consideration, and is enforceable on its own terms. Until all Indebtedness is paid in full, Guarantor waives any right to enforce any remedy Guarantor may have against the Borrower or any other guarantor, surety, or other person, and further, Guarantor waives any right to participate in any collateral for the Indebtedness now or hereafter held by Lender.

GUARANTOR’S UNDERSTANDING WITH RESPECT TO WAIVERS. Guarantor warrants and agrees that each of the waivers set forth above is made with Guarantor’s full knowledge of its significance and consequences and that, under the circumstances, the waivers are reasonable and not contrary to public policy or law. If any such waiver is determined to be contrary to any applicable law or public policy, such waiver shall be effective only to the extent permitted by law or public policy.

SUBORDINATION OF BORROWER’S DEBTS TO GUARANTOR. Guarantor agrees that the Indebtedness of Borrower to Lender, whether now existing or hereafter created, shall be superior to any claim that Guarantor may now have or hereafter acquire against Borrower, whether or not Borrower becomes insolvent. Guarantor hereby expressly subordinates any claim Guarantor may have against Borrower, upon any account whatsoever, to any claim that Lender may now or hereafter have against Borrower. In the event of insolvency and consequent liquidation of the assets of Borrower, through bankruptcy, by an assignment for the benefit of creditors, by voluntary liquidation, or otherwise, the assets of Borrower applicable to the payment of the claims of both Lender and Guarantor shall be paid to Lender and shall be first applied by Lender to the Indebtedness of Borrower to Lender. Guarantor does hereby assign to Lender all claims which it may have or acquire against Borrower or against any assignee or trustee in bankruptcy of Borrower; provided however, that such assignment shall be effective only for the purpose of assuring to Lender full payment in legal tender of the Indebtedness. If Lender so requests, any notes or credit agreements now or hereafter evidencing any debts or obligations of Borrower to Guarantor shall be marked with a legend that the same are subject to this Guaranty and shall be delivered to Lender. Guarantor agrees, and Lender is hereby authorized, in the name of Guarantor, from time to time to file financing statements and continuation statements and to execute documents and to take such other actions as Lender deems necessary or appropriate to perfect, preserve and enforce its rights under this Guaranty.

MISCELLANEOUS PROVISIONS. The following miscellaneous provisions are a part of this Guaranty:

Amendments. This Guaranty, together with any Related Documents, constitutes the entire understanding and agreement of the parties as to the matters set forth in this Guaranty. No alteration of or amendment to this Guaranty shall be effective unless given in writing and signed by the party or parties sought to be charged or bound by the alteration or amendment.

Attorneys’ Fees; Expenses. Guarantor agrees to pay upon demand all of Lender’s costs and expenses, including Lender’s attorneys’ fees and Lender’s legal expenses, incurred in connection with the enforcement of this Guaranty. Lender may hire or pay someone else to help enforce this Guaranty, and Guarantor shall pay the costs and expenses of such enforcement. Costs and expenses include Lender’s attorneys’ fees and legal expenses whether or not there is a lawsuit, including attorneys’ fees and legal expenses for bankruptcy proceedings (including efforts to modify or vacate any automatic stay or injunction), appeals, and any anticipated post-judgment collection services. Guarantor also shall pay all court costs and such additional fees as may be directed by the court.

Caption Headings. Caption headings in this Guaranty are for convenience purposes only and are not to be used to interpret or define the provisions of this Guaranty.

Governing Law. This Guaranty will be governed by, construed and enforced in accordance with federal law and the laws of the State of California. This Guaranty has been accepted by Lender in the State of California.

Choice of Venue. If there is a lawsuit, Guarantor agrees upon Lender’s request to submit to the jurisdiction of the courts of Los Angeles County, State of California.

Integration. Guarantor further agrees that Guarantor has read and fully understands the terms of this Guaranty; Guarantor has had the opportunity to be advised by Guarantor’s attorney with respect to this Guaranty; the Guaranty fully reflects Guarantor’s intentions and parol evidence is not required to interpret the terms of this Guaranty. Guarantor hereby indemnifies and holds Lender harmless from all losses, claims, damages, and costs (including Lender’s attorneys’ fees) suffered or incurred by Lender as a result of any breach by Guarantor of the warranties, representations and agreements of this paragraph.

Interpretation. In all cases where there is more than one Borrower or Guarantor, then all words used in this Guaranty in the singular shall be deemed to have been used in the plural where the context and construction so require; and where there is more than one Borrower named in this Guaranty or when this Guaranty is executed by more than one Guarantor, the words “Borrower” and “Guarantor” respectively shall mean all and any one or more of them. The words “Guarantor,” “Borrower,” and “Lender” include the heirs, successors, assigns, and transferees of each of them. If a court finds that any provision of this Guaranty is not valid or should not be enforced, that fact by itself will not mean that the rest of this Guaranty will not be valid or enforced. Therefore, a court will enforce the rest of the provisions of this Guaranty even if a provision of this Guaranty may be found to be invalid or unenforceable. If any one or more of Borrower or Guarantor are corporations, partnerships, limited liability companies, or similar entities, it is not necessary for Lender to inquire into the powers of Borrower or Guarantor or of the officers, directors, partners, managers, or other agents acting or purporting to act on their behalf, and any indebtedness made or created in reliance upon the professed exercise of such powers shall be guaranteed under this Guaranty.

Notices. Any notice required to be given under this Guaranty shall be given in writing, and, except for revocation notices by Guarantor, shall be effective when actually delivered, when actually received by telefacsimile (unless otherwise required by law), when deposited with a nationally recognized overnight courier, or, if mailed, when deposited in the United States mail, as first class, certified or registered mail postage prepaid, directed to the addresses shown near the beginning of this Guaranty. All revocation notices by Guarantor shall be in writing and shall be effective upon delivery to Lender as provided in the section of this Guaranty entitled “DURATION OF GUARANTY.” Any party may change its address for notices under this Guaranty by giving formal written notice to the other parties, specifying that the purpose of the notice is to change the party’s address. For notice purposes, Guarantor agrees to keep Lender informed at all times of Guarantor’s current address. Unless otherwise provided or required by law, if there is more than one Guarantor, any notice given by Lender to any Guarantor is deemed to be notice given to all Guarantors.

No Waiver by Lender. Lender shall not be deemed to have waived any rights under this Guaranty unless such waiver is given in writing and signed by Lender. No delay or omission on the part of Lender in exercising any right shall operate as a waiver of such right or any other right. A waiver by Lender of a provision of this Guaranty shall not prejudice or constitute a waiver of Lender’s right otherwise to demand strict compliance with that provision or any other provision of this Guaranty. No prior waiver by Lender, nor any course of dealing between Lender and Guarantor, shall constitute a waiver of any of Lender’s rights or of any of Guarantor’s obligations as to any future transactions. Whenever the consent of Lender is required under this Guaranty, the granting of such consent by Lender in any instance shall not constitute continuing consent to subsequent instances where such consent is required and in all cases such consent may be granted or withheld in the sole discretion of Lender.

Successors and Assigns. Subject to any limitations stated in this Guaranty on transfer of Guarantor’s interest, this Guaranty shall be binding upon and inure to the benefit of the parties, their successors and assigns.

FINANCIAL STATEMENT CERTIFICATIONS. The undersigned hereby certifies to California Bank & Trust (“Bank”) that all financial information (“Information”) submitted to Bank now and at all times during the terms of this loan does, and will, fairly and accurately represent the financial condition of the undersigned, all Borrowers and Guarantors. Financial Information includes, but is not limited to all Business Financial Statements (including Interim and Year-End financial statements that are company prepared and/or CPA-prepared), Business Income Tax Returns, Borrowing Base Certificates, Accounts Receivable and Accounts Payable Agings, Personal Financial Statements and Personal Income Tax Returns. The undersigned understands that the Bank will rely on all financial information, whenever provided, and that such information is a material inducement to Bank to make, to continue to make, or otherwise extend credit accommodations to the undersigned. The undersigned covenants and agrees to notify Bank of any adverse material changes in her/his/its financial condition in the future. The undersigned further understands and acknowledges that there are criminal penalties for giving false financial information to federally insured financial institutions.

DEPOSIT AGREEMENT SECURITY. Guarantor hereby grants a security interest to Lender in any and all deposit accounts (checking, savings, money market or time) of Guarantor at Lender, now existing or hereinafter opened, to secure its obligations hereunder. This includes all deposit accounts Guarantor holds jointly with someone else.

DEFINITIONS. The following capitalized words and terms shall have the following meanings when used in this Guaranty. Unless specifically stated to the contrary, all references to dollar amounts shall mean amounts in lawful money of the United States of America. Words and terms used in the singular shall include the plural, and the plural shall include the singular, as the context may require. Words and terms not otherwise defined in this Guaranty shall have the meanings attributed to such terms in the Uniform Commercial Code:

Borrower. The word “Borrower” means IRIS International, Inc. and includes all co-signers and co-makers signing the Note.

Guarantor. The word “Guarantor” means each and every person or entity signing this Guaranty, including without limitation Advanced Digital Imaging Research, LLC.

Guaranty. The word “Guaranty” means the guaranty from Guarantor to Lender, including without limitation a guaranty of all or part of the Note.

Indebtedness. The word “Indebtedness” means Borrower’s indebtedness to Lender as more particularly described in this Guaranty.

Lender. The word “Lender” means California Bank & Trust, its successors and assigns.

Note. The word “Note” means the promissory note dated May 25, 2004, in the original principal amount of $10,000,000.00 from Borrower to Lender, together with all renewals of, extensions of, modifications of, refinancings of, consolidations of, and substitutions for the promissory note or agreement.

Related Documents. The words “Related Documents” mean all promissory notes, credit agreements, loan agreements, environmental agreements, guaranties, security agreements, mortgages, deeds of trust, security deeds, collateral mortgages, and all other instruments, agreements and documents, whether now or hereafter existing, executed in connection with the Indebtedness.

EACH UNDERSIGNED GUARANTOR ACKNOWLEDGES HAVING READ ALL THE PROVISIONS OF THIS GUARANTY AND AGREES TO ITS TERMS. IN ADDITION, EACH GUARANTOR UNDERSTANDS THAT THIS GUARANTY IS EFFECTIVE UPON GUARANTOR’S EXECUTION AND DELIVERY OF THIS GUARANTY TO LENDER AND THAT THE GUARANTY WILL CONTINUE UNTIL TERMINATED IN THE MANNER SET FORTH IN THE SECTION TITLED “DURATION OF GUARANTY”. NO FORMAL ACCEPTANCE BY LENDER IS NECESSARY TO MAKE THIS GUARANTY EFFECTIVE. THIS GUARANTY IS DATED MAY 25, 2004.

LASER PRO Lending, Ver. 5.23.30.004 Copr, Harland Financial Solutions, Inc. 1997, 2004. All Rights Reserved. Ÿ CA

Promissory Note