<PAGE>
 
                                                                    Exhibit 10.3

                     SEVENTH AMENDMENT TO CREDIT AGREEMENT
                     -------------------------------------

     SEVENTH AMENDMENT TO CREDIT AGREEMENT (this "Amendment"), dated as of July
8, 1998, among DADE BEHRING HOLDINGS, INC. ("Holdings"), DADE BEHRING INC. (the
"Borrower"), the financial institutions party to the Credit Agreement referred
to below (the "Banks") and BANKERS TRUST COMPANY, as Agent (the "Agent") for the
Banks.  All capitalized terms used herein and not otherwise defined shall have
the respective meanings provided such terms in the Credit Agreement.

                              W I T N E S S E T H:
                              - - - - - - - - - - 

     WHEREAS, Holdings, the Borrower, the Banks and the Agent are parties to a
Credit Agreement, dated as of May 7, 1996 and amended and restated as of April
29, 1997 (as amended, modified, restated or supplemented to the date hereof, the
"Credit Agreement"); and

     WHEREAS, the parties hereto wish to amend the Credit Agreement as herein
provided;

     NOW, THEREFORE, it is agreed:

I.  Amendments to Credit Agreement.
    ------------------------------ 

          1.   Section 4.02(A)(c) of the Credit Agreement is hereby amended by
deleting the amount "$8,000,000" appearing in the first proviso to said Section
and inserting the amount "$25,000,000" in lieu thereof.

          2.   Section 8.02(p) of the Credit Agreement is hereby amended by
deleting the amount "$8,000,000" appearing in said Section and inserting the
amount $25,000,000" in lieu thereof.

II.  Miscellaneous Provisions.
     ------------------------ 

          1.   In order to induce the Banks to enter into this Amendment, the
Borrower hereby represents and warrants that:

          (a) no Default or Event of Default exists as of the Seventh Amendment
     Effective Date, both before and after giving effect to this Amendment; and

          (b) all of the representations and warranties contained in the Credit
     Agreement or the other Credit Documents are true and correct in all
     material respects on and as of the Seventh Amendment Effective Date, both
     before and after giving effect to this Amendment, with the same effect as
     though such representations and warranties had been made on and as of the
     Seventh
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     Amendment Effective Date (it being understood that any representation or
     warranty made as of a specific date shall be true and correct in all
     material respects as of such specific date).

          2.   This Amendment is limited as specified and shall not constitute a
modification, acceptance or waiver of any other provision of the Credit
Agreement or any other Credit Document.

          3.   This Amendment may be executed in any number of counterparts and
by the different parties hereto on separate counterparts, each of which
counterparts when executed and delivered shall be an original, but all of which
shall together constitute one and the same instrument.  A complete set of
counterparts shall be lodged with the Borrower and the Agent.

          4.   THIS AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES
HEREUNDER SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAW OF THE
STATE OF NEW YORK.

          5.   This Amendment shall become effective as of July 8, 1998 on the
date (the "Seventh Amendment Effective Date") when each of Holdings, the
Borrower and the Required Banks shall have signed a counterpart hereof (whether
the same or different counterparts) and shall have delivered (including by way
of facsimile transmission) the same to the Agent at its Notice Office.

          6.   From and after the Seventh Amendment Effective Date, all
references in the Credit Agreement and each of the other Credit Documents to the
Credit Agreement shall be deemed to be references to the Credit Agreement as
amended hereby.

                           *            *           *

                                      -2-
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          IN WITNESS WHEREOF, the parties hereto have caused their duly
authorized officers to execute and deliver this Amendment as of the date first
above written.

                                      DADE BEHRING HOLDINGS, INC.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Nancy A. Krejsa
                                      Title: Vice President & Treasurer
 
 
                                      DADE BEHRING INC.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Nancy A. Krejsa
                                      Title: Vice President & Treasurer
 
 
                                      BANKERS TRUST COMPANY,
                                      Individually, as Agent
                                      and as Collateral Agent
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Mary Kay Coyle
                                      Title: Managing Director
 
 
                                      THE BANK OF NOVA SCOTIA
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  F.C.H. Ashby
                                      Title: Senior Manager Loan Operations
 
 
                                      BANK OF TOKYO-MITSUBISHI
                                      TRUST COMPANY
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Peter Stearn
                                      Title: Vice President
 
 

                                      -3-
<PAGE>
 
                                      BANKBOSTON, N.A.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Marie C. Duprey
                                      Title  Vice President
 
 
                                      GENERAL ELECTRIC CAPITAL
                                      CORPORATION
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Holly Kaczmarczyk
                                      Title: Duly Authorized Signatory
 
 
                                      SANWA BUSINESS CREDIT CORPORATION
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Michael J. Cox
                                      Title: First Vice President
 
 
                                      ABN AMRO BANK N.V., Chicago Branch
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  John E. Robertson
                                      Title: Vice President
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Mary L. Honda
                                      Title: Vice President
 
 
                                      AG CAPITAL FUNDING PARTNERS, L.P.
                                      By: Angelo, Gordon & Co., L.P., as
                                      Investment Advisor
 
 

                                      -4-
<PAGE>
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Jeffrey H. Aronson
                                      Title: Managing Director
 
 
                                      CITIBANK, N.A.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Steven Kaufman
                                      Title: Vice President
 
 
                                      CITY NATIONAL BANK
 
 
                                      By/s/
                                        -------------------------------------- 
                                      Name:  Scott Kelley
                                      Title: Vice President
 
 
                                      CREDIT AGRICOLE INDOSUEZ
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  David Bouhl, F.V.P.
                                      Title: Head of Corporate Banking Chicago
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Katherine L. Abbott
                                      Title: First Vice President
 
 
                                      OCTAGON CREDIT INVESTORS LOAN
                                      PORTFOLIO, a Unit of The Chase
                                      Manhattan Bank
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  James P. Ferguson
                                      Title: Managing Director

                                      -5-
<PAGE>
 
                                      CRESCENT/MACH I PARTNERS, L.P.
                                      By TCW Asset Management Company,
                                      its Investment Manager
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Justin L. Driscoll
                                      Title: Senior Vice President
 
 
                                      STRATA FUNDING LTD.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  John H. Cullinane
                                      Title: Director
 
 
                                      CERES FINANCE LTD.
 
 
                                      By/s/
                                        --------------------------------------  
                                      Name:  John H. Cullinane
                                      Title: Director
 
 
                                      AERIES FINANCE LTD.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Andrew Ian Wignall
                                      Title: Director
 
 
                                      CAPTIVA FINANCE LTD.
 
 
                                      By/s/
                                        -------------------------------------- 
                                      Name:  John H. Cullinane
                                      Title: Director
 
 
                                      CAPTIVA II FINANCE LTD.
 
 
                                      By/s/
                                        --------------------------------------

                                      Name:  John H. Culinane
                                      Title: Director
 

                                      -6-
<PAGE>
 
                                      CITY NATIONAL BANK
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Scott Kelley
                                      Title: Vice President
 
 
                                      CREDIT AGRICOLE INDOSUEZ
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Katherine L. Abbott
                                      Title: First Vice President
 
 
                                      By/s/
                                        --------------------------------------  
                                      Name:  David Bouhl, F.V.P.
                                      Title: Head of Corporate Banking Chicago
 
 
                                      CRESCENT/MACH I PARTNERS, L.P.
                                      By TCW Asset Management Company,
                                      its Investment Manager
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:
                                      Title:
 
 
                                      DAI-ICHI KANGYO BANK LTD.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Sunao Hirata
                                      Title: Vice President
 

                                      -7-
<PAGE>
 
                                      FIRST NATIONAL BANK OF CHICAGO


                                      By/s/
                                        --------------------------------------
                                      Name:  Christopher Cavaiani
                                      Title: Vice President
 
 
                                      THE FUJI BANK, LIMITED
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Tetsuo Kamatsu (K-219)
                                      Title: Joint General Manager
 
 
                                      GT GLOBAL FLOATING RATE FUND
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:
                                      Title:
 
 
                                      IMPERIAL BANK
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  R. Vadalma
                                      Title: Senior Vice President
 
 
                                      KEYPORT LIFE INSURANCE COMPANY
                                      By:  Stein, Roe & Farnham, as Investment
                                      Advisor
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Brian G. Good
                                      Title: Vice President & Portfolio Manager
 
 
                                      MERRILL LYNCH DEBT STRATEGIES
                                      PORTFOLIO
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:
                                      Title:

                                      -8-
<PAGE>
 
                                      MERRILL LYNCH PRIME RATE PORTFOLIO
                                      By:  Merrill Lynch Asset Management L.P.,
                                      as Investment Advisor
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:
                                      Title:
 
 
                                      MERRILL LYNCH SENIOR FLOATING RATE
                                      FUND, INC.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:
                                      Title:
 
 
                                      ML CBO IV (CAYMAN) LTD.
                                      By: Protective Asset Management Company,
                                          as Collateral Manager
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:
                                      Title:
 
 
                                      OCTAGON LOAN TRUST
                                      By: Octagon Credit Investors, its Manager
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  James P. Ferguson
                                      Title: Managing Director

                                      -9-
<PAGE>
 
                                      PILGRIM AMERICA PRIME RATE TRUST
                                      By: PILGRIM AMERICA INVESTMENTS, INC.,
                                      as its Investment Manager
 
 

                                      By/s/
                                        --------------------------------------
                                      Name:  Jeffrey A. Bakalar
                                      Title: Vice President
 
 
                                      MORGAN STANLEY DEAN WITTER
                                      PRIME INCOME TRUST
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Peter Gewirtz
                                      Title: Authorized Signatory
 
 
                                      SAKURA BANK LTD.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Brian G. Good
                                      Title: Vice President & Portfolio Manager
 
 
                                      ROYALTON COMPANY,
                                      By: Pacific Investment Management Company,
                                      as its Investment Advisor
                                      By:  PIMCO Management inc., as general
                                      partner
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:
                                      Title:
 
 
                                      SOCIETE GENERALES
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  John M. Stack
                                      Title: Director
 

                                      -10-
<PAGE>
 
                                      SOUTHERN PACIFIC BANK
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:
                                      Title:
 
 
                                      AERIES FINANCE LTD.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Andrew Ian Wignall
                                      Title: Director
 
 
                                      CAPTIVA FINANCE LTD.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  David Egglishaw
                                      Title: Director
 
 
                                      CAPTIVA II FINANCE LTD.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  David Egglishaw
                                      Title: Director
 
 
                                      CERES FINANCE LTD.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  David Egglishaw
                                      Title: Director
 
 
                                      STRATA FUNDING LTD.
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  David Egglishaw
                                      Title: Director

                                      -11-
<PAGE>
 
                                      VAN KAMPEN AMERICAN CAPITAL PRIME
                                      RATE INCOME TRUST
 
 
                                      By/s/
                                        --------------------------------------
                                      Name:  Jeffrey W. Maillet
                                      Title: Senior Vice President & Director

                                      -12-