<PAGE>

                                                                    EXHIBIT 2.28

                             SUPPLEMENTAL INDENTURE

     THIS SUPPLEMENTAL INDENTURE is dated as of December 23, 2004, by and among
FRESENIUS MEDICAL CARE AG (the "Company"), a German stock corporation
(Aktiengesellschaft), U.S. BANK NATIONAL ASSOCIATION, a national banking
association, as successor trustee to STATE STREET BANK AND TRUST COMPANY, a
Massachusetts chartered trust company, as trustee (the "Trustee"), FMC TRUST
FINANCE S.A.R.L. LUXEMBOURG-III, a Luxembourg private limited company ("LuxCo"),
FRESENIUS MEDICAL CARE HOLDINGS, INC., a New York corporation, and FRESENIUS
MEDICAL CARE DEUTSCHLAND GMBH, a German private limited company, and is made
with reference to that certain Senior Subordinated Indenture dated as of June
15, 2001 by and among the Company, Luxco, as Issuer, State Street Bank and Trust
Company as trustee and the Guarantors named therein, (the "Indenture").
Capitalized terms used and not defined herein shall have the meanings ascribed
to such terms in the Indenture.

                                    RECITALS

     WHEREAS, the Company desires to assume the obligations of the Note Issuer
pursuant to Section 8.4 of the Indenture;

     WHEREAS, an Opinion of Counsel, in the form required pursuant to Sections
1.2, 8.4 and 9.3 has been delivered to the Trustee simultaneously with the
execution and delivery hereof; and

     WHEREAS, an Officers' Certificate, in the form required pursuant to
Sections 1.2 and 9.3 has been delivered to the Trustee simultaneously with the
execution and delivery hereof.

     NOW, THEREFORE, for and in consideration of the promises and of the mutual
covenants herein contained and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties agree as
follows:

                                   ARTICLE I

                            Supplement to Indenture

     SECTION 1.01.  Assumption of Obligations of the Note Issuer by the
Company.  The Company hereby assumes and agrees to perform the obligations of
the Note Issuer under the Securities and the Indenture and subjects itself to
all of the provisions (including the representations and warranties) of the
Indenture as the Note Issuer.

     SECTION 1.02.  Release of LuxCo.  Pursuant to Section 8.4 of the Indenture,
upon the execution of this Supplemental Indenture by the Trustee the Company
shall succeed to, and be substituted for, and may exercise every right and power
of the Note Issuer under the Indenture with the same effect as if it were the
Note Issuer thereunder, and LuxCo shall be discharged from all obligations and
covenants under the Indenture and the Securities.

     SECTION 1.03.  References to the Note Issuer and the Company.  In order to
effect the assumption by the Company of the obligations of the Note Issuer, the
Indenture is hereby amended and supplemented as follows:

          (a) Except as provided in paragraph (b) below, each reference in the
     Indenture to the Note Issuer in its capacity as primary Obligor of the
     Securities or issuer of the Securities shall henceforth be deemed to be a
     reference to the Company as issuer of the Securities, and each other
     reference to "the Company" shall remain a reference to the Company;

          (b) Each reference in the Indenture to "the Note Issuer and the
     Company" or to "the Note Issuer or the Company" shall henceforth be a
     reference to the Company.
<PAGE>

     SECTION 1.04.  Full Force and Effect of Other Guarantees.  Fresenius
Medical Care Holdings, Inc. and Fresenius Medical Care Deutschland GmbH each
acknowledges and agrees that its Guaranty shall continue in full force and
effect and that all of its obligations thereunder shall be valid and enforceable
and shall not be impaired or limited by the execution or effectiveness of this
Supplemental Indenture.

                                   ARTICLE II

                         Form of Security and Guaranty

     Pursuant to Section 2.1 of the Indenture, new forms of Security and
Guaranty are hereby established, in the forms annexed as Annex A and Annex B
hereto, respectively, conforming with the amendments to the Indenture set forth
herein; provided that the existing certificates evidencing Securities and the
Guaranty endorsed thereon shall continue to represent the Securities and the
Guaranty, as amended hereby, until actually replaced.

                                  ARTICLE III

                                 Miscellaneous

     SECTION 3.01.  Section 9.1 of the Indenture.  This Supplemental Indenture
is a supplemental indenture pursuant to Section 9.1 of the Indenture. Upon
execution and delivery of this Supplemental Indenture, the terms and conditions
of this Supplemental Indenture shall be part of the terms and conditions of the
Indenture for any and all purposes, and all the terms and conditions of both
shall be read together as though they constitute one and the same instrument,
except that in case of conflict, the provisions of this Supplemental Indenture
will control.

     SECTION 3.02.  Full Force and Effect.  Except as they have been modified in
this Supplemental Indenture, each and every term and provision of the Indenture
shall continue in full force and effect, and all references to the Indenture in
the Indenture shall be deemed to mean the Indenture as supplemented and amended
pursuant hereto.

     SECTION 3.03.  Counterparts.  This Supplemental Indenture may be executed
in any number of counterparts and in separate counterparts, each of which when
so executed shall be deemed to be an original, but all of which counterparts
shall together constitute but one and the same instrument.

     SECTION 3.04.  Governing Law.  This Supplemental Indenture shall be
governed by and construed in accordance with the laws of the State of New York
without giving effect to principles of conflicts of laws.

     SECTION 3.05.  Headings.  The headings of the Articles and Sections of this
Supplemental Indenture have been inserted for convenience of reference only, and
are not to be considered a part hereof and shall in no way modify or restrict
any of the terms and provisions hereof.

     SECTION 3.06.  Recitals of the Company, the Note Issuer and the
Guarantors.  The recitals contained herein and, upon issuance, in the form of
Security and Guaranty annexed hereto, except the Trustee's certificate of
authentication, shall be taken as the statements of the Company, the Note Issuer
or the Guarantors, as the case may be, and the Trustee assumes no responsibility
for their correctness. The Trustee makes no representations as to, and assumes
no responsibility for, the validity of this Supplemental Indenture.

        [The remainder of this page has been intentionally left blank.]

                                        2
<PAGE>

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

                                          FRESENIUS MEDICAL CARE AG

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                                          FMC TRUST FINANCE S.A.R.L.
                                          LUXEMBOURG-III

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                                          FRESENIUS MEDICAL CARE HOLDINGS, INC.
                                          as a Subsidiary Guarantor

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                                          FRESENIUS MEDICAL CARE DEUTSCHLAND
                                          GMBH, as a Subsidiary Guarantor

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                                        3
<PAGE>

                                          U.S. BANK NATIONAL
                                          ASSOCIATION, as Trustee

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                                        4
<PAGE>

                                    ANNEX A

                                FORM OF SECURITY

Form of Face of Security

                           FRESENIUS MEDICAL CARE AG

               7 3/8% SENIOR SUBORDINATED NOTES DUE JUNE 15, 2011
                     GUARANTEED AS TO PAYMENT OF PRINCIPAL,
            PREMIUM, IF ANY, AND INTEREST BY CERTAIN SUBSIDIARIES OF
                           FRESENIUS MEDICAL CARE AG
No.                                                                  E

     FRESENIUS MEDICAL CARE AG, a corporation organized and existing under the
laws of Germany (hereinafter called the "Company", which term includes any
successor corporation under the Indenture hereinafter referred to), for value
received, hereby promises to pay to U.S. BANK NATIONAL ASSOCIATION, as Preferred
Trustee for Fresenius Medical Care Capital Trust V, or registered assigns, the
principal sum of           Thousand Euro on June 15, 2011. The Company further
promises to pay interest on said principal sum quarterly in arrears on March 14,
June 14, September 14 and December 14 of each year, commencing September 14,
2001, (each such date, an "Interest Payment Date") (provided, however, that
interest paid on such Interest Payment Dates will accrue through March 15, June
15, September 15, and December 15, respectively) at the rate of 7 3/8% per
annum, (plus Additional Amounts and Additional Sums, if any) until the principal
hereof is paid or duly provided for or made available for payment and on any
overdue principal and (without duplication and to the extent that payment of
such interest is enforceable under applicable law) on any interest which is in
arrears more than a quarter at the rate of 7 3/8% per annum, compounded
quarterly. The amount of interest payable for any period shall be computed on
the basis of twelve 30-day months and a 360-day year. The amount of interest
payable for any partial period shall be computed on the basis of the number of
days elapsed in a 360-day year of twelve 30-day months. In the event that any
date on which interest is payable on this Security is not a Business Day, then a
payment of the interest payable on such date will be made on the immediately
preceding Business Day (and interest shall accrue for the period from and after
such immediately preceding Business Day through such Interest Payment Date,
Redemption Date or Stated Maturity, as the case may be, (in each case with the
same force and effect as if made on the Interest Payment Date or Redemption Date
or at the Stated Maturity)). A "Business Day" shall mean any day other than (i)
a Saturday or Sunday, (ii) a day on which banking institutions in London, New
York City, Frankfurt am Main or Luxembourg are authorized or required by law or
executive order to remain closed, (iii) a day on which the Trans-European
Automated Real-Time Gross-settlement Express Transfer System is authorized or
required by law to close, or (iv) a day on which the Corporate Trust Office of
the Trustee, or, with respect to the Preferred Securities, the principal office
of the Preferred Trustee under the Declaration hereinafter referred to for
Fresenius Medical Care Capital Trust V, is closed for business. The interest so
payable, and punctually paid or duly provided for, on any Interest Payment Date
will, as provided in the Indenture, be paid to the Person in whose name this
Security (or one or more Predecessor Securities, as defined in the Indenture) is
registered at the close of business on the Regular Record Date for such
interest, which shall be the date which is the fourteenth day immediately
preceding such Interest Payment Date (whether or not a Business Day). Any
interest not so punctually paid or duly provided for shall forthwith cease to be
payable to the Holder on such Regular Record Date and may either be paid to the
Person in whose name this Security (or one or more Predecessor Securities) is
registered at the close of business on a Special Record Date for the payment of
such Defaulted Interest to be fixed by the Trustee, notice whereof shall be
given to Holders not less than 10 days prior to such Special Record Date, or be
paid in any other lawful manner not inconsistent with the requirements of any
securities exchange on which the Securities may be listed, and upon such notice
as may be required by such exchange, all as more fully provided in said
Indenture.

     Payments on this Security issued as a Global Security shall be made in
immediately available funds to the Depositary. In the event that this Security
is issued in certificated form, the principal of (and premium, if

                                        1
<PAGE>

any) and interest (including Additional Sums and Additional Amounts, if any) on
the Security will be payable at the office maintained by the Company under the
Indenture; provided, that unless the Security is held by the Trust or any
permissible successor entity as provided under the Declaration in the event of a
merger, consolidation or amalgamation of the Trust, payment of interest may be
made at the option of the Company by check mailed to the address of the person
entitled thereto, as such address shall appear in the Register.

     The indebtedness evidenced by this Security is, to the extent provided in
the Indenture, subordinate and subject in right of payment to the prior payment
in full of all Senior Indebtedness, and this Security is issued subject to the
provisions of the Indenture with respect thereto. Each Holder of this Security,
by accepting the same, (a) agrees to and shall be bound by such provisions, (b)
authorizes and directs the Trustee on his behalf to take such actions as may be
necessary or appropriate to effectuate the subordination so provided and (c)
appoints the Trustee his attorney-in-fact for any and all such purposes. Each
Holder hereof, by his acceptance hereof, waives all notice of the acceptance of
the subordination provisions contained herein and in the Indenture by each
holder of Senior Indebtedness, whether now outstanding or hereafter incurred,
and waives reliance by each such holder upon said provisions.

     Reference is hereby made to the further provisions of this Security set
forth on the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

     Unless the certificate of authentication hereon has been executed by the
Trustee referred to on the reverse hereof by manual signature, this Security
shall not be entitled to any benefit under the Indenture or be valid or
obligatory for any purpose.

                                        2
<PAGE>

     IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed.

     Dated:           , 200

                                          FRESENIUS MEDICAL CARE AG

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                    TRUSTEE'S CERTIFICATE OF AUTHENTICATION

     This is one of the Securities with the Guaranties endorsed thereon referred
to in the within-mentioned Indenture.

                                          U.S. BANK NATIONAL ASSOCIATION,
                                          TRUSTEE

                                          By:
                                            ------------------------------------
                                                     Authorized Officer

                                        3
<PAGE>

Form of Reverse of Security

     This Security is one of a duly authorized issue of securities of the
Company (herein called the "Securities"), issued under a Senior Subordinated
Indenture, dated as of June 15, 2001 as amended by the Supplemental Indenture
dated as of December   , 2004 (the "Indenture"), between the Company, as issuer,
and U.S. Bank National Association, as successor trustee to State Street Bank
and Trust Company, as Trustee (herein called the "Trustee", which term includes
any successor trustee under the Indenture), Fresenius Medical Care Holdings,
Inc. and Fresenius Medical Care Deutschland GmbH, as Guarantors, to which
Indenture and all indentures supplemental thereto reference is hereby made for a
statement of the respective rights, limitations of rights, duties and immunities
thereunder of the Trustee, the Company, and the Holders of the Securities, and
of the terms upon which Securities are, and are to be, authenticated and
delivered.

     All terms used in this Security that are defined in the Indenture and in
the Amended and Restated Declaration of Trust, dated as of June 15, 2001, (the
"Declaration"), for Fresenius Medical Care Capital Trust V, shall have the
meanings assigned to them in the Indenture or the Declaration, as the case may
be.

     If a Tax Event or an Investment Company Event in respect of the Trust shall
occur and be continuing, the Company shall cause the Trustees (as defined in the
Declaration) to dissolve the Trust and cause the Securities to be distributed to
the holders of the Trust Securities in dissolution of the Trust or, in the event
of a Tax Event only, may cause the Securities to be redeemed, in each case,
subject to and in accordance with the provisions of the Declaration, within 90
days following the occurrence of such Tax Event or Investment Company Event. The
Securities may be redeemed, at the option of the Company, subject to the
provisions of Article XI of the Indenture, at any time as a whole but not in
part, at 100% of the principal amount thereof, plus accrued and unpaid interest
(if any) to the date of redemption (subject to the right of Holders of record on
the relevant Regular Record Date to receive interest due on the relevant
Interest Payment Date), in the event the Company has become or would become
obligated to pay, on the next date on which any amount would be payable with
respect to the Securities, any Additional Amounts as a result of a change in or
an amendment to the laws (including any regulations promulgated thereunder) of
the United States, Germany, the United Kingdom or the jurisdiction of formation
of the issuer of the Securities (initially, Luxembourg) (or any political
subdivision or taxing authority thereof or therein), or any change in or
amendment to any official position regarding the application or interpretation
of such laws or regulations, which change or amendment is announced or becomes
effective on or after the date of the issuance of the Securities (other than, in
either case, any amendment or change implementing, complying with, or introduced
in order to conform to, or otherwise arising as a result of or in connection
with, any European Union Directive on the taxation of savings implementing the
conclusions of the ECOFIN Council meeting of 26-27 November 2000).

     The Securities do not have the benefit of any sinking fund obligations.

     If an Event of Default shall occur and be continuing, the principal of all
the Securities may be declared due and payable in the manner, with the effect
and subject to the conditions provided in the Indenture.

     As provided in the Indenture and subject to certain limitations therein set
forth, the obligations of the Company under the Indenture and this Security are
Guaranteed on a senior subordinated basis pursuant to Guaranties endorsed
hereon. The Indenture provides that a Guarantor shall be released from its
Guaranty upon compliance with certain conditions.

     The Indenture contains provisions for satisfaction, discharge and
defeasance at any time of the entire indebtedness of this Security upon
compliance by the Company with certain conditions set forth in the Indenture.

     The Indenture permits, with certain exceptions as therein provided, the
Company, the Guarantors and the Trustee at any time to enter into a supplemental
indenture or indentures for the purpose of modifying in any manner the rights
and obligations of the Company, the Guarantors and of the Holders of the
Securities, with the consent of the Holders of not less than a majority in
principal amount of the Outstanding Securities to be affected by such
supplemental indenture. The Indenture also contains provisions permitting
Holders of specified percentages in aggregate outstanding principal amount of
the Outstanding Securities affected thereby, on behalf of the Holders of all the
Securities, to waive compliance by the Company or the Guarantors

                                        4
<PAGE>

with certain provisions of the Indenture and certain past defaults under the
Indenture and their consequences. Any such consent or waiver by the Holder of
this Security shall be conclusive and binding upon such Holder and upon all
future Holders of this Security and of any Security issued upon the registration
of transfer hereof or in exchange herefor or in lieu hereof, whether or not
notation of such consent or waiver is made upon this Security.

     As provided in and subject to the provisions of the Indenture, if an Event
of Default with respect to the Securities at the time Outstanding occurs and is
continuing, then and in every such case the Trustee or the Holders of not less
than 25% in aggregate outstanding principal amount of the Outstanding Securities
may declare the principal amount of and interest (including Additional Sums and
Additional Amounts, if any) on all the Securities to be due and payable
immediately, by a notice in writing to the Company and the Guarantors (and to
the Trustee if given by Holders), provided, that if the Trustee or such Holders
fail to do so, the Preferred Trustee shall have such right by a notice in
writing to the Company and the Trustee; and upon any such declaration such
specified amount of and the accrued interest (including Additional Sums and
Additional Amounts, if any) on all the Securities shall become immediately due
and payable, provided, that the payment of principal and interest (including
Additional Sums and Additional Amounts, if any) on such Securities shall remain
subordinated to the extent provided in Article XII of the Indenture.

     No reference herein to the Indenture and no provision of this Security or
of the Indenture shall alter or impair the obligation of the Company, which is
absolute and unconditional, to pay the principal of (and premium, if any) and
interest on this Security at the times, place and rate, and in the coin or
currency, herein prescribed.

     As provided in the Indenture and subject to certain limitations therein set
forth, the transfer of this Security is registrable in the Securities Register,
upon surrender of this Security for registration of transfer at the office or
agency of the Company maintained under Section 10.2 of the Indenture duly
endorsed by, or accompanied by a written instrument of transfer in form
satisfactory to the Company and the Securities Registrar duly executed by, the
Holder hereof or his attorney duly authorized in writing, and thereupon one or
more new Securities, of authorized denominations and for the same aggregate
principal amount, will be issued to the designated transferee or transferees. No
service charge shall be made for any such registration of transfer or exchange,
but the Company may require payment of a sum sufficient to cover any tax or
other governmental charge payable in connection therewith.

     Prior to due presentment of this Security for registration of transfer, the
Company, the Guarantors, the Trustee and any agent of the Company, the
Guarantors or the Trustee may treat the Person in whose name this Security is
registered as the owner hereof, for all purposes (subject to certain limitations
set forth in the Indenture), whether or not this Security be overdue, and
neither the Company, the Guarantors, the Trustee nor any such agent shall be
affected by notice to the contrary.

     The Securities are issuable only in registered form without coupons in
denominations of E1,000 and any integral multiple thereof. As provided in the
Indenture and subject to certain limitations therein set forth, the Securities
are exchangeable for a like aggregate principal amount of Securities of a
different authorized denomination, as requested by the Holder surrendering the
same.

     The Company and, by its acceptance of this Security or a beneficial
interest therein, the Holder of, and any Person that acquires a beneficial
interest in, this Security agree that for German and U.S. Federal, state and
local tax purposes and for purposes of any tax imposed by the jurisdiction of
formation of the issuer of the Securities, or any political subdivision or
taxing authority thereof or therein, it is intended that this Security
constitute indebtedness.

     All terms used in this Security which are defined in the Indenture shall
have the meanings assigned to them in the Indenture.

     THE INDENTURE AND THIS SECURITY SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD TO CONFLICT OF
LAWS PRINCIPLES THEREOF.

                                        5
<PAGE>

                                    ANNEX B

                                FORM OF GUARANTY

     For value received, each of the Guarantors hereby jointly and severally
unconditionally Guarantees, on a senior subordinated basis, to each Holder of a
Security authenticated and delivered by the Trustee, and to the Trustee on
behalf of such Holder, the due and punctual payment of the principal of (and
premium, if any) and interest (including Additional Sums and Additional Amounts,
if any) on such Security when and as the same shall become due and payable,
whether at the Stated Maturity, by acceleration, call for redemption, purchase
or otherwise, in accordance with the terms of such Security and of this
Indenture. In case of the failure of the Company punctually to make any such
payment, each of the Guarantors hereby jointly and severally agrees to cause
such payment to be made punctually when and as the same shall become due and
payable, whether at the Stated Maturity or by acceleration, call for redemption,
purchase or otherwise, and as if such payment were made by the Company. The
Guarantee extends to the Company's repurchase obligations arising from a Change
of Control or an Asset Disposition pursuant to the Indenture.

     Each of the Guarantors hereby jointly and severally agrees that its
obligations hereunder shall be unconditional, irrespective of the validity,
regularity or enforceability of such Security or this Indenture, the absence of
any action to enforce the same, any exchange, release or non-perfection of any
Lien on any collateral for, or any release or amendment or waiver of any term of
any other Guarantee of, or any consent to departure from any requirement of any
other Guarantee of all or any of the Securities, the election by the Trustee or
any of the Holders in any proceeding under Chapter 11 of Title 11 of the United
States Code (the "Bankruptcy Code") of the application of Section 1111(b)(2) of
the Bankruptcy Code, or equivalent provision under applicable law, any borrowing
or grant of a security interest by the Company, as debtor-in-possession, under
Section 364 of the Bankruptcy Code, or equivalent provision under applicable
law, the disallowance, under Section 502 of the Bankruptcy Code, or other
similar applicable law, of all or any portion of the claims of the Trustee or
any of the Holders for payment of any of the Securities, any waiver or consent
by the Holder of such Security or by the Trustee with respect to any provisions
thereof or of the Indenture, the obtaining of any judgment against the Company
or any action to enforce the same or any other circumstances which might
otherwise constitute a legal or equitable discharge or defense of a guarantor.
Each of the Guarantors hereby waives the benefits of diligence, presentment,
demand for payment, any requirement that the Trustee or any of the Holders
protect, secure, perfect or insure any security interest in or other Lien on any
property subject thereto or exhaust any right or take any action against the
Company or any other Person or any collateral, filing of claims with a court in
the event of insolvency or bankruptcy of the Company, any right to require a
proceeding first against the Company, protest or notice with respect to such
Security or the Indebtedness evidenced thereby and all demands whatsoever, and
covenants that this Guaranty will not be discharged in respect of such Security
except by complete performance of the obligations contained in such Security and
in this Guaranty. Each of the Guarantors hereby agrees that, in the event of a
default in payment of principal (or premium, if any) or interest (including
Additional Sums and Additional Amounts, if any) on such Security, whether at
their Stated Maturity, by acceleration, call for redemption, purchase or
otherwise, legal proceedings may be instituted by the Trustee on behalf of, or
by, the Holder of such Security, subject to the terms and conditions set forth
in the Indenture, directly against each of the Guarantors to enforce this
Guaranty without first proceeding against the Company. Each Guarantor agrees
that, to the extent permitted by law, if, after the occurrence and during the
continuance of an Event of Default, the Trustee or any of the Holders are
prevented by applicable law from exercising their respective rights to
accelerate the maturity of the Securities, to collect interest on the
Securities, or to enforce or exercise any other right or remedy with respect to
the Securities, or the Trustee or the Holders are prevented from taking any
action to realize on any collateral, such Guarantor agrees to pay to the Trustee
for the account of the Holders, upon demand therefor, the amount that would
otherwise have been due and payable had such rights and remedies been permitted
to be exercised by the Trustee or any of the Holders.

     The indebtedness of each Guarantor evidenced by this Guaranty is, to the
extent provided in the Indenture, subordinate and subject in right of payment to
the prior payment in full of all Senior Indebtedness of such Guarantor, and this
Guaranty is issued subject to the provisions of the Indenture with respect
thereto. Each Holder of this Security, by accepting the same, (a) agrees to and
shall be bound by such provisions,

                                        1
<PAGE>

(b) authorizes and directs the Trustee on his behalf to take such action as may
be necessary or appropriate to effectuate the subordination so provided and (c)
appoints the Trustee his attorney-in-fact for any and all such purposes.

     No reference herein to the Indenture and no provision of this Guaranty or
of the Indenture shall alter or impair the Guaranty of any Guarantor, which is
absolute and unconditional, of the due and punctual payment of the principal
(and premium, if any) and interest (including Additional Sums and Additional
Amounts, if any) on the Security upon which this Guaranty is endorsed.

     Each Guarantor shall be subrogated to all rights of the Holder of this
Security against the Company in respect of any amounts paid by such Guarantor on
account of this Security pursuant to the provisions of its Guaranty or the
Indenture; provided, however, that such Guarantor shall not be entitled to
enforce or to receive any payments arising out of, or based upon, such right of
subrogation until the principal of (and premium, if any) and interest on this
Security and all other Securities issued under the Indenture shall have been
paid in full.

     This Guaranty shall remain in full force and effect and continue to be
effective should any petition be filed by or against the Company for liquidation
or reorganization, or equivalent proceeding under applicable law, should the
Company become insolvent or make an assignment for the benefit of creditors or
should a receiver or trustee be appointed for all or any significant part of the
Company's assets, or the equivalent of any of the foregoing under applicable
law, and shall, to the fullest extent permitted by applicable law, continue to
be effective or be reinstated, as the case may be, if at any time payment and
performance of the Securities is, pursuant to applicable law, rescinded or
reduced in amount, or must otherwise be restored or returned by any obligee on
the Securities whether as a voidable preference, fraudulent transfer, or as
otherwise provided under similar laws affecting the rights of creditors
generally or under applicable laws of the jurisdiction of formation of the
Company, all as though such payment or performance had not been made. In the
event that any payment, or any part thereof, is rescinded, reduced, restored or
returned, the Securities shall, to the fullest extent permitted by applicable
law, be reinstated and deemed reduced only by such amount paid and not so
rescinded, reduced, restored or returned.

     The Guarantors shall have the right to seek contribution from any
non-paying Guarantor so long as the exercise of such right does not impair the
rights of the Holders under this Guaranty.

     The Guarantors or any particular Guarantor shall be released from this
Guaranty upon the terms and subject to certain conditions provided in the
Indenture.

     By delivery of a supplemental indenture to the Trustee in accordance with
the terms of the Indenture or the execution of a Guaranty Agreement, each Person
that becomes, or assumes the obligations of, a Guarantor after the date of the
Indenture will be deemed to have executed and delivered this Guaranty for the
benefit of the Holder of this Security with the same effect as if such Guarantor
was named below.

     All terms used in this Guaranty which are defined in the Indenture referred
to in the Security upon which this Guaranty is endorsed shall have the meanings
assigned to them in such Indenture.

     This Guaranty shall not be valid or obligatory for any purpose until the
certificate of authentication on the Security upon which this Guaranty is
endorsed shall have been executed by the Trustee under the Indenture by manual
signature.

     Each Guaranty will be limited in amount to an amount not to exceed the
maximum amount that can be guaranteed by the applicable Guarantor without
rendering the Guaranty, as it relates to such Guarantor, voidable under
applicable law relating to fraudulent conveyance or fraudulent transfer or
similar laws affecting the rights of creditors generally or under applicable law
of Germany.

     In the case of Fresenius Medical Care Deutschland GmbH ("FMCD"), the
following provisions apply:

     A Profit and Loss Pooling Agreement (the "Agreement")
(Ergebnisabfuhrungsvertrag) between the Company and FMCD dated as of August 21,
1996 was entered into the commercial register with effect from January 1, 1996.
FMCD, having a stated capital of DM 80 million, had a capital reserve account of

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<PAGE>

DM 168,302,162 (the "January 1, 1996 Amount") in its balance sheet as of January
1, 1996. Assuming that the January 1, 1996 Amount has not decreased by losses in
the business of FMCD since January 1, 1996, at least such amount exceeds the
Company's assets protecting its share capital within the meaning of Section 30
of the German GmbH Law. Since January 1, 1996, the January 1, 1996 Amount has
not been decreased by the actions of the Company (the sole shareholder of FMCD),
e.g. no distributions against the January 1, 1996 Amount have been made.

     Based thereon, the guaranty obligations of FMCD hereunder and under FMCD's
guaranty of the 9% Notes, the 2008 7 3/8% Notes, the 2008 7 7/8% Notes, the 2011
7 7/8% Notes and any other Senior Subordinated Indebtedness, if any, of FMCD to
which Section 30 of the German GmbH law may apply are limited to the amount of
the capital reserves of FMCD as of the date hereof less its obligations as a
guarantor from time to time under the Senior Credit Agreement (the "Minimum
Guaranty Amount"). If, in the case of a default under the Indenture, the capital
reserves are higher than such Minimum Guaranty Amount, such higher amount (the
"Higher Guaranty Amount") shall serve as limitation to the obligations of FMCD,
as Guarantor. In case FMCD, as Guarantor, has to sell off assets to fulfil its
obligations under the Indenture, after such guaranty obligations have been
drawn, and if the proceeds from the sale of such assets exceed the amount of
their book value, such excess amounts shall be paid to the Trustee for the
benefit of the Holders, subject to the provisions of Article XIV hereof, in
addition to the Minimum Guaranty Amount or the Higher Guaranty Amount,
respectively. For the determination of the applicable book value, the book value
of assets which were included into the balance sheet per January 1, 1996
applies, and for such assets which were not yet included but added to the
business of FMCD since that date, the book value on the day of the sale of such
assets applies. Should Section 30 of the German GmbH law however require a lower
Minimum Guaranty Amount or a lower Higher Guaranty Amount, then such lower
amounts required by law shall be applicable.

     FMCD undertakes not to decrease its capital reserves, neither by capital
increase from such reserve accounts nor by other kinds of contributions to its
shareholders or affiliates without the prior written approval of the Holders of
a majority in principal amount of the Outstanding Securities.

     FMCD undertakes to maintain a profit and loss pooling agreement with the
Company during the term of the Indenture, in particular, to extend the term of
such agreement to the term of the Indenture and not to terminate, rescind or
amend such agreement without prior notice to the Trustee and the consent of the
Holders of a majority in principal amount of the Outstanding Securities thereto.
In case of a termination of such profit and loss pooling agreement, FMCD will
grant, upon the request of the Holders of a majority in principal amount of the
Outstanding Securities, collateral to minimize the legal and financial
disadvantages caused by the termination of such agreement, as far as legally
available under German law. FMCD undertakes to give notice immediately to the
Trustee if it intends to give notice of termination to such agreement or to
agree to the termination of such agreement, or if it becomes aware that the
Company intends to terminate such agreement. During the term of the profit and
loss pooling agreement, any and all allocations of profit to the Company and any
and all cash distributions to the Company as a consequence thereof upon the
terms and conditions of the profit and loss pooling agreement are permitted and
unrestricted, subject to the terms of Section 30 of the German GmbH law as
described above.

     Reference is made to Article XIII and Article XIV of the Indenture for
further provisions with respect to this Guaranty.

     THIS GUARANTY SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
LAWS OF THE STATE OF NEW YORK WITHOUT GIVING EFFECT TO PRINCIPLES OF CONFLICT OF
LAWS.

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     IN WITNESS WHEREOF, each of the undersigned has caused this instrument to
be duly executed.

                                          FRESENIUS MEDICAL CARE
                                          HOLDINGS, INC.

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                                          FRESENIUS MEDICAL CARE
                                          DEUTSCHLAND GMBH

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

                                          By:
                                            ------------------------------------
                                              Name:
                                            Title:

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