SECOND SUPPLEMENTAL INDENTURE

Exhibit 4.1

SENIOR

SECOND SUPPLEMENTAL INDENTURE

THIS SECOND FIRST SUPPLEMENTAL INDENTURE (the “Supplemental Indenture”) dated as of the 9th day of February 2007, among DaVita Inc., a Delaware corporation (the “Company”), the Guarantors (as defined below), the persons named as Additional Guarantors signatory hereto (the “Additional Guarantors”) and The Bank of New York Trust Company, N.A., as Trustee (the “Trustee”), amends and supplements the Indenture dated as of March 22, 2005 among the Company, the Guarantors named therein, as guarantors (the “Guarantors”), and the Trustee (the “Original Indenture”) with respect to the Company’s 6 ⁵/8% Senior Notes due 2013, as amended and supplemented by that certain First Supplemental Indenture dated as of October 5, 2005 among the Company, the Guarantors and the Trustee.

W I T N E S S E T H:

WHEREAS, the Additional Guarantors are, simultaneously herewith, entering into a Guarantee with respect to certain Indebtedness of the Company and the Original Indenture provides that upon entering into any such Guarantee the Additional Guarantors shall enter into a supplemental indenture agreeing to guarantee the obligations of the Company under the Original Indenture;

NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE WITNESSETH:

For and in consideration of the premises, it is mutually covenanted and agreed, for the equal and proportionate benefit of the Holders of Notes, as follows:

Section 1. Defined Terms. All terms used in this Supplemental Indenture which are defined in the Original Indenture have the meanings assigned to them in the Original Indenture.

Section 2. Additional Guarantors. Pursuant to Section 4.19 of the Original Indenture, each of the Additional Guarantors hereby, jointly and severally, unconditionally and irrevocably Guarantees, on a senior basis, the full and prompt payment of the principal of, premium, if any, and interest on the Notes and all other obligations of the Company (including, without limitation, to the Trustee and to the Holders of the Notes) under the Original Indenture on the terms and subject to the conditions set forth in the Original Indenture and agrees to be bound as a Guarantor under the Original Indenture. In connection herewith, each Additional Guarantor will execute and deliver to the Trustee a notation of Note Guarantee.

Section 3. Miscellaneous.

(a) The Article and Section headings herein are for convenience only and shall not affect the construction hereof.

(b) In case any one or more of the provisions in this Supplemental Indenture shall be invalid, illegal or unenforceable, the validity, legality, and enforceability of any such provision in every other respect and of the remaining provisions shall not in any way be affected or impaired thereby, it being intended that all of the provisions hereof shall be enforceable to the full extent permitted by law.

(c) This Supplemental Indenture will be governed by and construed in accordance with the laws of the State of New York, as applied to contracts made and performed within the State of New York, without regard to principles of conflicts of laws.

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(d) Except as amended or supplemented by this Supplemental Indenture, the terms, conditions, covenants and agreements set forth in the Original Indenture shall continue in full force and effect.

(e) This Supplemental Indenture may be executed in any number of counterparts, each of which so executed shall be deemed to be an original, but all such counterparts shall together constitute but one and the same instrument.

(f) The Trustee makes no representations as to the validity or sufficiency of this Supplemental Indenture. The recitals and statements herein are deemed to be those of the Company and the Additional Guarantors and not of the Trustee.

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SENIOR

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the day and year first above written.