1
                                                                     Exhibit 8.1




August 2, 2001                                                   OUR FILE NUMBER
                                                                     285,846-055
                                                                    NY1-815328.1
Fresenius Medical Care AG
FMC Trust Finance S.a.r.l. Luxembourg- III                  WRITER'S DIRECT DIAL
Fresenius Medical Care Capital Trust IV                             212-326-2003
Fresenius Medical Care Capital Trust V
Else-Kroner Strasse 1                                    WRITER'S E-MAIL ADDRESS
61346 Bad Hamburg v.d. H                                       jgiannola@omm.com
Germany


            RE:   FRESENIUS MEDICAL CARE CAPITAL TRUST IV
                  FRESENIUS MEDICAL CARE CAPITAL TRUST V

Ladies and Gentlemen:

            You have requested our opinion as to whether Fresenius Medical Care
Capital Trust IV ("Trust IV") and Fresenius Medical Care Capital Trust V ("Trust
V", and together, the "Trusts") will continue to qualify as grantor trusts for
United States federal income tax purposes after the exchange of trust preferred
securities, as described below.

            Each of the Trusts is a statutory business trust formed under the
laws of the State of Delaware pursuant the declarations of trust, as amended
(individually, the "Amended Declaration" and collectively, the "Amended
Declarations") entered into between FMC Trust Finance S.a.r.l. Luxembourg- III
(the "Company"), Fresenius Medical Care AG ("FMC AG"), a stock corporation
(Aktiengesellschaft) organized under the laws of the Federal Republic of
Germany) and sole shareholder of the Company, State Street Bank and Trust
Company, as Preferred trustee, First Union Trust Company National Association,
as Delaware trustee, the Company trustees and the holders from time to time. At
the time of formation of each of the Trusts and the initial issuance of the
trust preferred securities, the Company and each of the Trusts agreed, pursuant
to the Registration Rights Agreements dated as of June 6, 2001, in the case of
Trust IV and dated as of June 15, 2001, in the case of Trust V, to file and use
their best efforts to cause a registration statement to become effective with
respect to the exchange of new trust preferred securities for old trust
preferred securities, in each case with identical terms in all material
respects. The Company and the Trusts are now registering new trust preferred
securities for each of the Trusts.
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August 2, 2001 - Page 2


            In rendering our opinion, we have examined the Registration
Statement on Form F-4 in the form filed with the SEC on August 2, 2001 (the
"Registration Statement") and the preliminary prospectus (the "Prospectus")
included therein, and such other documents as we have deemed necessary or
appropriate for purposes of our opinion. For purposes of such examination, we
have assumed the genuineness of all signatures, the legal capacity of natural
persons, and the authenticity of all documents submitted to us as relevant to
this opinion and, as to matters of fact, we have relied upon the agreements,
instruments, certificates and documents referred to above. We have also assumed
(a) that all parties have the corporate power and authority to enter into and
perform all obligations thereunder; (b) the due authorization by all requisite
corporate actions, the due execution and delivery and the validity, binding
effect and enforceability of such documents; and (c) that each of the Trusts is
organized, is operating and will continue to be operated in accordance with the
Delaware Business Trust Act and the terms and conditions of its respective
Amended Declaration. Finally, we have assumed that the form of documents
reviewed for this opinion will be executed in the form in which we reviewed them
in all material respects. Capitalized terms used herein shall have the meanings
ascribed to them in the Registration Statement unless otherwise indicated.

            Trust IV is offering to exchange up to US$225 million aggregate
liquidation amount of new U.S. dollar-denominated 7-7/8% trust preferred
securities ("New USD Trust Preferred Securities") that have been registered with
the Securities and Exchange Commission for a like aggregate liquidation amount
of old U.S. dollar-denominated 7-7/8% trust preferred securities ("Old USD Trust
Preferred Securities"). To the extent that this exchange offer (the "USD
Exchange Offer") is accepted, the Company will also exchange its new U.S.
dollar-denominated 7-7/8% Senior Subordinated Notes (the "New USD Notes") for a
like principal amount of old U.S. dollar-denominated 7-7/8% Senior Subordinated
Notes (the "Old USD Notes").

            Trust V is offering to exchange up to E300 million aggregate
liquidation amount of new Euro-denominated 7-3/8% trust preferred securities
("New Euro Trust Preferred Securities" and collectively with the New USD Trust
Preferred Securities, the "New Trust Preferred Securities") that have been
registered with the Securities and Exchange Commission for a like aggregate
liquidation amount of old Euro-denominated 7-3/8% trust preferred securities
("Old Euro Trust Preferred Securities", and collectively with the Old USD Trust
Preferred Securities, the "Old Trust Preferred Securities"). To the extent that
this exchange offer (the "Euro Exchange Offer," and collectively with the USD
Exchange Offer, the "Exchange Offers") is accepted, the Company will also
exchange its new Euro denominated 7-3/8% Senior Subordinated Notes (the "New
Euro Notes" and collectively with the New USD Notes, the "New Notes") for a like
principal amount of Euro-denominated 7-3/8% Senior Subordinated Notes (the "Old
Euro Notes" and collectively with the Old USD Notes, the "Old Notes").

            Finally, the guarantees of FMC AG with respect to the New Trust
Preferred Securities will be exchanged for like guarantees with respect to the
Old Trust Preferred Securities. The Note Guarantors will also exchange their
guarantees with respect to the New Notes for like guarantees with respect to the
Old Notes.
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August 2, 2001 - Page 3


            The New USD Trust Preferred Securities are identical to the Old USD
Trust Preferred Securities that they replace, and the New Euro Trust Preferred
Securities are identical to the Old Euro Trust Preferred Securities that they
replace, except that, in each case (i) the new Trust Preferred Securities have
been registered and, therefore, will not be subject to certain restrictions on
transfer, and (ii) the New Trust Preferred Securities will not contain the
minimum liquidation amount transfer restrictions and will not provide for any
increase in the distribution rate thereon. In addition, the terms of the New
Notes are the same in all material respects as the terms of the Old Notes that
they replace, except that, in each case (a) the New Notes will not contain the
minimum principal amount transfer restrictions, and (b) the New Notes will not
provide for any increase in the interest rate thereon.

            In connection with the Exchange Offers, we are advised that (a)
there will be no change in the amount of the Common Securities for each Trust ,
which will continue to be owned by FMC AG, and (b) the Trust Preferred
Securities and Common Securities of each Trust will continue to represent all of
the beneficial interests in the assets of each Trust. In addition, the only
assets of each Trust will continue to be either the Old Notes with respect to
that Trust and/or the New Notes with respect to that Trust, and the Trustees of
each Trust will continue to be prohibited from varying those assets.

            The Common Securities of each Trust will continue to rank pari passu
with the Old Trust Preferred Securities and/or the New Trust Preferred
Securities of that Trust, except that, with respect to each Trust, upon the
occurrence and during the continuance of a Declaration Event of Default for that
Trust (as defined in each Amended Declaration), the rights of the Company as
holder of that Trust's Common Securities to payment in respect of distributions
and payments upon liquidation, redemption and otherwise will be subordinated to
the rights of the holders of that Trust's Trust Preferred Securities. In
addition, upon the occurrence and during the continuance of a Declaration Event
of Default, the rights of the Common Securities holder under the separate
payment guarantee of FMC AG will continue to be subordinated to the rights of
the holders of the Old Trust Preferred Securities and the New Trust Preferred
Securities of that Trust with respect to distributions from that Trust. Finally,
the voting rights of the holders of the Old Trust Preferred Securities, the New
Trust Preferred Securities and the Common Securities of each Trust remain the
same.

            Our opinion set forth herein is based on existing provisions of the
Internal Revenue Code of 1986, as amended (the "Code"), Treasury Department
Regulations promulgated thereunder (the "Regulations"), administrative
interpretations of the Internal Revenue Service (the "IRS") and judicial
decisions. The opinion expressed herein deals only with United States federal
income taxation and only with respect to the matters addressed herein and not
with state or local taxation or the matters of any other taxing jurisdiction. In
addition, changes in the law, facts, or representations relied upon could
possibly adversely affect the conclusions reached in this opinion. Consequently,
future events may result in federal income tax treatment of a Trust and its
beneficial owners that is materially and adversely different from that described
herein.
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August 2, 2001 - Page 4


            Under Section 301.7701-4(c)(1) of the Regulations, an investment
trust will not be classified as a trust if there is a power under the trust
agreement to vary the investment of the trust certificate holders. The exchange
of the New Trust Preferred Securities for the Old Preferred Securities, and of
the New Notes for the Old Notes, with respect to each Trust is being made
pursuant to the provisions of the Rights Agreements entered into at the time the
Old Trust Preferred Securities were issued. In addition, except for the
provisions noted above (which are no longer applicable to the registered
securities), the terms of the New Trust Preferred Securities are identical to
the terms of the Old Preferred Securities and the terms of the New Notes are
identical to the terms of the Old Notes with respect to each Trust. Accordingly,
the exchange of a Trust's trust preferred securities and notes will not cause a
Trust to fail to qualify as a trust under the Regulations as a result of any
investment powers conferred on the Trustees by an Amended Declaration.

            In addition, since the terms of the Common Securities has not
changed and since the terms of the New Trust Preferred Securities are in all
material respects the same as the terms of the Old Trust Preferred Securities
with respect to a Trust, the existence of multiple classes of securities in a
Trust should continue to be treated as merely incidental to facilitating direct
investment in the Old Notes and/or the New Notes with respect to that Trust.
Regulations Section 301.7701-4(c)(1). The subordination of certain payment
rights of the Common Securities holders to the trust preferred securities
holders, as well as the subordination feature of the Common Securities holder's
guarantee, which will only apply upon the occurrence and during the continuance
of a Declaration Event of Default, should also be treated, under the
Regulations, as incidental to each Trust's purpose of facilitating direct
investment in its respective Old Notes and/or New Notes. See Example 2 of
Regulations Section 301.7701-4(c); see also Priv. Ltr. Rul. 9132027 (May 8,
1991) (a trust certificate holder's guarantee of trust distributions to other
certificate holders, and the subordination of the guarantor's right to
distributions in favor of the other certificate holders upon default of the
underlying loans, was incidental to the trust's purpose of facilitating direct
investment in the trust assets); Priv. Ltr. Rul. 9244036 (August 5, 1992) (a
limited guarantee by one class of trust certificate holders in favor of another
class is incidental to facilitating direct investment in trust assets); and
Priv. Ltr. Rul. 9140076 (July 9, 1991) (to the same effect). While these private
rulings may not be relied upon by taxpayers other that the taxpayer to whom the
ruling is addressed, they do indicate the IRS's thinking on this issue.

            While it is still not clear that the existence of the limited voting
rights of the Common Securities holder, and of the trust preferred securities
holders under various circumstances, would cause a Trust to be viewed, under the
Regulations, as having two classes of ownership interest, even if it did, in our
view any such limited voting rights would also be deemed to be "incidental"
under the Regulations.

            Based on the foregoing, it is our opinion that, for federal income
tax purposes, each Trust will continue to be classified as a grantor trust, and
not as an association taxable as a corporation.
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August 2, 2001 - Page 5


            We hereby confirm the tax consequences set forth in the Registration
Statement under the heading "Tax Considerations - United States", and we consent
to the filing of this opinion as an exhibit to the Registration Statement and to
the reference to our firm under the heading "Tax Considerations - United States"
in the in prospectus forming a part thereof.


                                       Respectfully submitted,



                                       /s/ O'MELVENY & MYERS LLP

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