<PAGE>   1

                                                                   EXHIBIT 10.8



                                 AMENDMENT NO. 7
                                       TO
                                CREDIT AGREEMENT


     THIS AMENDMENT NO. 7 TO CREDIT AGREEMENT ("AMENDMENT") is dated as of May
31, 2000, by and among METAL MANAGEMENT, INC., a Delaware corporation ("MTLM"),
each of the corporations and other entities set forth on EXHIBIT A hereto (MTLM
and each of such corporations and other entities sometimes hereinafter are
referred to individually as a "BORROWER" and collectively as "BORROWERS"); MTLM,
acting in its capacity as funds administrator for itself and the other Borrowers
(in such capacity, the "FUNDS ADMINISTRATOR"); BT COMMERCIAL CORPORATION, a
Delaware corporation (in its individual capacity, hereinafter referred to as
"BTCC"), and the other financial institutions signatories hereto as lenders
(BTCC and each of such other financial institutions hereinafter are referred to
individually as a "LENDER" and collectively as "LENDERS"); and BTCC, acting in
its capacity as agent (in such capacity, hereinafter referred to as the "AGENT")
for itself and the other Lenders. Capitalized terms used herein but not
otherwise defined herein shall have the respective meanings assigned to such
terms in the Credit Agreement.


                                   WITNESSETH:

     WHEREAS, the Borrowers, the Funds Administrator, the Agent and the Lenders
have entered into that certain Credit Agreement dated as of March 31, 1998, as
amended (the "CREDIT AGREEMENT"), pursuant to which the Lenders have agreed to
make certain loans and other financial accommodations to or for the account of
the Borrowers;

     WHEREAS, the respective Borrowers have requested that the Agent and the
Lenders further amend the Credit Agreement; and

     WHEREAS, the Agent and the Lenders have agreed to further amend the Credit
Agreement on the terms and subject to the conditions hereinafter set forth;

     NOW, THEREFORE, in consideration of the premises set forth above, the terms
and conditions contained herein, and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the respective parties
hereto hereby agree as follows:

     AMENDMENT TO CREDIT AGREEMENT. Effective as of the date hereof, upon
satisfaction of the conditions precedent set forth in SECTION 2 below, and in
reliance upon the representations and warranties of the respective Borrowers and
the Funds Administrator set forth herein, the Credit Agreement is hereby amended
as follows:

     1.1 The definition of the term "Applicable Margin" set forth in SECTION 1.1
of the Credit Agreement is hereby deleted in its entirety and the following
language is hereby substituted therefor:

         APPLICABLE MARGIN shall mean (I) with respect to any Prime Rate Loan,
     one


<PAGE>   2



     and one-half percent (1.50%) and (II) with respect to any LIBOR Rate Loan,
     two and one-half percent (2.50%).

     1.2 The definition of the term "Expiration Date" set forth in SECTION 1.1
of the Credit Agreement is hereby deleted in its entirety and the following
language is hereby substituted therefor:

     EXPIRATION DATE means March 31, 2004.

     1.3 The following defined term is hereby inserted in SECTION 1.1 of the
Credit Agreement in the appropriate alphabetical order:

     SEVENTH AMENDMENT EFFECTIVE DATE means May 31, 2000.

     1.4 SECTION 6.11 of the Credit Agreement is hereby amended by deleting
the words "the Closing Date" set forth in the first line thereof and
substituting therefor the words "the Seventh Amendment Effective Date."

     1.5 SECTION 7.4 of the Credit Agreement is hereby amended by deleting
the parenthetical set forth therein in its entirety and substituting therefor
the following language:

     (except that any Borrower or any wholly-owned Subsidiary of any Borrower
     may merge with, or be dissolved into, any other Borrower, PROVIDED, THAT
     the Agent receives five (5) Business Days' prior written notice thereof)

     1.6 SECTION 8.6 of the Credit Agreement is hereby amended by deleting
CLAUSE (C) thereof in its entirety and substituting therefor the following
language:

     (C) in connection with the merger or dissolution of any Borrower or any
     wholly-owned Subsidiary of any Borrower into any other Borrower,

     1.7 SECTION 8.7 of the Credit Agreement is hereby amended by deleting
CLAUSE (V) thereof in its entirety and substituting therefor the following
language:

         (V) MTLM may make regularly scheduled payments of interest on the
     Subordinated Notes, so long as, in the case of each such payment,
     immediately before and after giving effect thereto, no Default or Event of
     Default shall have occurred and be continuing;

     1.8 SECTION 8.7 of the Credit Agreement is hereby amended by (I) inserting
the following language therein immediately following CLAUSE (VI) thereof and
(II) redesignating CLAUSE (VII) thereof as clause "(viii)":

         (VII) so long as, in each case, before and after giving effect to each
     such


                                                                              2



<PAGE>   3





     repurchase, no Default or Event of Default shall have occurred and be
     continuing, MTLM may repurchase shares of its capital stock for the purpose
     of redistributing such shares to management and other employees of the
     respective Credit Parties pursuant to a management stock option plan or
     similar employee incentive program duly established by the Board of
     Directors of MTLM (an "EMPLOYEE INCENTIVE PLAN"); PROVIDED, that (1) the
     aggregate consideration paid in connection with all such repurchases shall
     not exceed $2,000,000 and (2) concurrently with the making of any such
     repurchase, the Funds Administrator shall have delivered to the Agent a
     certificate executed by a Responsible Officer of the Funds Administrator,
     certifying (X) the total consideration paid in connection with such
     repurchase, together with a brief description thereof, and (Y) that the
     shares of capital stock so repurchased were repurchased solely for the
     purpose of redistributing such shares to management and other employees of
     the respective Credit Parties pursuant to an Employee Incentive Plan; and

     1.9  SECTION 8.8(G)(II) of the Credit Agreement is hereby amended by
deleting the reference to "1.0 to 1.0" set forth therein and substituting
therefor a reference to "1.4 to 1.0."

     1.10 ANNEX I of the Credit Agreement is hereby deleted in its entirety and
EXHIBIT B attached hereto ("AMENDED ANNEX I") is hereby substituted therefor.
Each of the Lenders hereby acknowledges and agrees that, upon effectiveness of
this Amendment, such Lender's Commitment shall be as set forth on Amended Annex
I.

     1.11 PART 6.10(A), 6.10(B) AND 6.11 OF SCHEDULE B (DISCLOSURE SCHEDULES) to
the Credit Agreement are hereby deleted in their entirety and the respective
Schedules attached as EXHIBIT C hereto are hereby substituted therefor.

     CONDITIONS PRECEDENT. This Amendment shall become effective as of the date
hereof, upon satisfaction of each of the following conditions:

         (A) the Agent shall have received a copy of this Amendment, duly
     executed and delivered by the all of the Lenders, each of the Borrowers and
     the Funds Administrator; and

         (B) the Agent shall have received in immediately available funds
     payment of all Fees due and payable under the Credit Documents on or prior
     to the date hereof.

     REPRESENTATIONS, WARRANTIES AND COVENANTS.

         3.1 Each of the Borrowers and the Funds Administrator hereby
     represents and warrants to the Agent and each of the Lenders that, after
     before and after giving effect to this Amendment:

             (A) All representations and warranties contained in the Credit
         Agreement and the other Credit Documents are true and correct in all
         material


                                                                              3


<PAGE>   4



         respects on and as of the date of this Amendment, in each case as if
         then made, other than representations and warranties that expressly
         relate solely to an earlier date (in which case such representations
         and warranties remain true and accurate on and as of such earlier
         date);

             (B) No Default or Event of Default has occurred which is
         continuing;

             (C) This Amendment, and the Credit Agreement, as amended hereby,
         constitute legal, valid and binding obligations of the Borrowers and
         the Funds Administrator, respectively, and are enforceable against
         each of the Borrowers and the Funds Administrator in accordance with
         their respective terms; and

             (D) The execution and delivery by the Borrowers and the Funds
         Administrator of this Amendment does not require the consent or
         approval of any Person, except such consents and approvals as have
         been obtained.

     REFERENCE TO AND EFFECT ON THE CREDIT AGREEMENT AND THE OTHER CREDIT
DOCUMENTS.

         4.1 Upon the effectiveness of this Amendment, each reference in the
     Credit Agreement to "this Agreement", "hereunder", "hereof", "herein" or
     words of like import, and each reference in each of the other Credit
     Documents to the "Credit Agreement" shall in each case mean and be a
     reference to the Credit Agreement as amended hereby.

         4.2 Except as expressly set forth herein, (I) the execution and
     delivery of this Amendment shall in no way affect any of the respective
     rights, powers or remedies of the Agent or any of the Lenders with respect
     to any Event of Default nor constitute a waiver of any provision of the
     Credit Agreement or any of the other Credit Documents and (II) all of the
     respective terms and provisions of the Credit Agreement, the other Credit
     Documents and all other documents, instruments, amendments and agreements
     executed and/or delivered by any of the Borrowers and/or the Funds
     Administrator pursuant thereto or in connection therewith shall remain in
     full force and effect and are hereby ratified and confirmed in all
     respects. The execution and delivery of this Amendment by the Agent and
     each of the Lenders shall in no way obligate the Agent or any of the
     Lenders, at any time hereafter, to consent to any other amendment or
     modification of any term or provision of the Credit Agreement or any of the
     other Credit Documents, whether of a similar or different nature.

     GOVERNING LAW. THE VALIDITY, INTERPRETATION AND ENFORCEMENT OF THIS
AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE INTERNAL
LAWS AND DECISIONS OF THE STATE OF ILLINOIS, WITHOUT REGARD TO CONFLICT OF LAWS
PRINCIPLES.


                                                                              4

<PAGE>   5


     HEADINGS. Section headings in this Amendment are included herein for
convenience of reference only and shall not constitute a part of this Amendment
for any other purpose.

     COUNTERPARTS. This Amendment may be executed in any number of counterparts
and by the different parties hereto in separate counterparts, each of which when
so executed and delivered shall be an original, but all of which shall together
constitute one and the same instrument. Any such counterpart which may be
delivered by facsimile transmission shall be deemed the equivalent of an
originally signed counterpart and shall be fully admissible in any enforcement
proceedings regarding this Agreement.



      [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK; SIGNATURE PAGES FOLLOW]




                                                                              5

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     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and delivered by their proper and duly authorized officers as of
the date first set forth above.

                                 BT COMMERCIAL CORPORATION, in its
                                 individual capacity as a Lender and in its
                                 capacity as Agent


                                 By:    /s/ Steve Friedlander
                                        -----------------------------
                                 Name:      Steve Friedlander
                                 Title:     Vice President



                                 BANKERS TRUST COMPANY, in its capacity
                                 as successor Agent

                                 By:    /s/ Sam Cardone
                                        -----------------------------
                                 Name:      Sam Cardone
                                 Title:     Director
<PAGE>   7



                                 HELLER FINANCIAL, INC.


                                 By: /s/ Albert J. Forzano
                                    ------------------------------
                                 Name:  Albert J. Forzano
                                 Title: Vice President



<PAGE>   8



                                 FLEET CAPITAL CORPORATION


                                 By: /s/ Robert J. Lund
                                    -----------------------------
                                 Name:  Robert J. Lund
                                 Title: Vice President



<PAGE>   9




                                 LASALLE NATIONAL BANK


                                 By: /s/ Michael J. Vercota
                                    -----------------------------
                                 Name:  Michael J. Vercota
                                 Title: Assistant Vice President




<PAGE>   10




                                 CONGRESS FINANCIAL CORP. (CENTRAL)


                                 By:    /s/ Andrew J. Heinz
                                        -----------------------------
                                 Name:      Andrew J. Heinz
                                 Title:     Vice President




<PAGE>   11




                                 FINOVA CAPITAL CORPORATION


                                 By: /s/ Bruce J. Mettel
                                    -----------------------------
                                 Name:  Bruce J. Mettel
                                 Title: Vice President




<PAGE>   12




                                 PNC BUSINESS CREDIT


                                 By: /s/ James M. Steffy
                                    -----------------------------
                                 Name:  James M. Steffy
                                 Title: Vice President




<PAGE>   13




                                 IBJ WHITEHALL BUSINESS CREDIT
                                 CORPORATION


                                 By:      /s/ Manuel R. Borges
                                        ------------------------------
                                 Name:        Manuel R. Borges
                                 Title:       Assistant Vice President



<PAGE>   14




                                 NATIONAL BANK OF CANADA


                                 By: /s/ Leroy A. Irvin
                                    -----------------------------
                                 Name:  Leroy A. Irvin
                                 Title: Vice President & Manager



                                 By: /s/ Thomas W. Buda, Jr.
                                    -----------------------------
                                 Name:  Thomas W. Buda, Jr.
                                 Title: Vice President
<PAGE>   15




                                 METAL MANAGEMENT, INC., a Delaware
                                 corporation, in its individual capacity as
                                 a Borrower and in its capacity as Funds
                                 Administrator


                                 By:      /s/ Robert C. Larry
                                        -----------------------------
                                 Name:        Robert C. Larry
                                 Title:       EVP and CFO




<PAGE>   16


                                 CALIFORNIA METALS RECYCLING, INC.
                                 CIM TRUCKING, INC.
                                 FERREX TRADING CORPORATION
                                 FIRMA, INC.
                                 FIRMA PLASTIC CO., INC.
                                 FPX, INC.
                                 HOUSTON COMPRESSED STEEL CORPORATION
                                 HOUTEX METALS COMPANY, INC.
                                 MAC LEOD METALS CO.
                                 MTLM ARIZONA, INC.
                                 METAL MANAGEMENT AEROSPACE, INC.
                                 METAL MANAGEMENT ALABAMA, INC.
                                 METAL MANAGEMENT ARIZONA, L.L.C.
                                 METAL MANAGEMENT CONNECTICUT, INC.
                                 METAL MANAGEMENT INDIANA, INC.
                                 METAL MANAGEMENT GULF COAST, INC.
                                 METAL MANAGEMENT MEMPHIS, L.L.C.
                                 METAL MANAGEMENT MIDWEST, INC.
                                 METAL MANAGEMENT MISSISSIPPI, L.L.C.
                                 METAL MANAGEMENT NORTHEAST, INC.
                                 METAL MANAGEMENT OHIO, INC.
                                 METAL MANAGEMENT PITTSBURGH, INC.
                                 METAL MANAGEMENT REALTY, INC.
                                 METAL MANAGEMENT SERVICES, INC.
                                 METAL MANAGEMENT STAINLESS & ALLOY, INC.
                                 METAL MANAGEMENT WEST, INC.
                                 METAL MANAGEMENT WEST COAST HOLDINGS, INC.
                                 METAL MANAGEMENT S&A HOLDINGS, INC.
                                 PROLER SOUTHWEST INC.
                                 P. JOSEPH IRON & METAL, INC.
                                 TROJAN TRADING CO.


                                 By: /s/ Robert C. Larry
                                    --------------------------------
                                 Name:  Robert C. Larry
                                 Title: Vice President



<PAGE>   17




                                 RESERVE IRON & METAL LIMITED
                                   PARTNERSHIP

                                 By:  P. JOSEPH IRON & METAL, INC., its
                                      general partner


                                 By:      /s/ Robert C. Larry
                                        -----------------------------
                                 Name:        Robert C. Larry
                                 Title:       VP




<PAGE>   18


                                    EXHIBIT A
                                       TO
                                 AMENDMENT NO.7
                            DATED AS OF MAY 31, 2000

                                 OTHER BORROWERS

1.   CALIFORNIA METALS RECYCLING, INC.
2.   CIM TRUCKING, INC.
3.   FERREX TRADING CORPORATION
4.   FIRMA, INC.
5.   FIRMA PLASTIC CO., INC.
6.   FPX, INC.
7.   HOUSTON COMPRESSED STEEL CORPORATION
8.   HOUTEX METALS COMPANY, INC.
9.   MAC LEOD METALS CO.
10.  MTLM ARIZONA, INC.
11.  METAL MANAGEMENT AEROSPACE, INC.
12.  METAL MANAGEMENT ALABAMA, INC.
13.  METAL MANAGEMENT ARIZONA, L.L.C.
14.  METAL MANAGEMENT CONNECTICUT, INC.
15.  METAL MANAGEMENT INDIANA, INC.
16.  METAL MANAGEMENT GULF COAST, INC.
17.  METAL MANAGEMENT MEMPHIS, L.L.C.
18.  METAL MANAGEMENT MIDWEST, INC.
19.  METAL MANAGEMENT MISSISSIPPI, L.L.C.
20.  METAL MANAGEMENT NORTHEAST, INC.
21.  METAL MANAGEMENT OHIO, INC.
22.  METAL MANAGEMENT PITTSBURGH, INC.
23.  METAL MANAGEMENT REALTY, INC.
24.  METAL MANAGEMENT SERVICES, INC.
25.  METAL MANAGEMENT STAINLESS & ALLOY, INC.
26.  METAL MANAGEMENT WEST, INC.
27.  METAL MANAGEMENT WEST COAST HOLDINGS, INC.
28.  METAL MANAGEMENT S&A HOLDINGS, INC.
29.  P. JOSEPH IRON & METAL,  INC.
30.  PROLER SOUTHWEST INC.
31.  RESERVE IRON & METAL LIMITED PARTNERSHIP
32.  TROJAN TRADING CO.



<PAGE>   19


EXHIBIT B
TO
AMENDMENT NO.7
DATED AS OF MAY 31, 2000

AMENDED ANNEX I TO CREDIT AGREEMENT

ATTACHED.




<PAGE>   20


                                     ANNEX I
                                       TO
                                CREDIT AGREEMENT
                           DATED AS OF MARCH 31, 1998

                      LIST OF LENDERS; COMMITMENT AMOUNTS;
                           APPLICABLE LENDING OFFICES


1.       BT COMMERCIAL CORPORATION
         233 South Wacker Drive
         Suite 8400 - Sears Tower
         Chicago, IL 60606

         COMMITMENT AMOUNT:                          $61,670,000

         DOMESTIC LENDING OFFICE:           233 South Wacker Drive
                                                     Suite 8400 - Sears Tower
                                                     Chicago, IL 60606

         LIBOR LENDING OFFICE:                       233 South Wacker Drive
                                                     Suite 8400 - Sears Tower
                                                     Chicago, IL 60606

2.       CONGRESS FINANCIAL CORP.
         (CENTRAL)
         150 South Wacker Drive
         Suite 2200
         Chicago, IL 60606-4401

         COMMITMENT AMOUNT:                          $30,000,000

         DOMESTIC LENDING OFFICE:           150 South Wacker Drive
                                                     Suite 2200
                                                     Chicago, IL 60606-4401

         LIBOR LENDING OFFICE:                       150 South Wacker Drive
                                                     Suite 2200
                                                     Chicago, IL 60606-4401

3.       FINOVA CAPITAL CORPORATION
         311 Wacker Drive
         Suite 4400
         Chicago, IL 60606-6618

         COMMITMENT AMOUNT:                          $20,000,000




<PAGE>   21


         DOMESTIC LENDING OFFICE:           311 Wacker Drive
                                                     Suite 4400
                                                     Chicago, IL 60606-6618

         LIBOR LENDING OFFICE:                       311 Wacker Drive
                                                     Suite 4400
                                                     Chicago, IL 60606-6618

4.       FLEET CAPITAL CORPORATION
         20800 Swenson Drive
         Suite 350
         Waukesha, WI 53186

         COMMITMENT AMOUNT:                          $31,665,000

         DOMESTIC LENDING OFFICE:           20800 Swenson Drive
                                                     Suite 350
                                                     Waukesha, WI 53186

         LIBOR LENDING OFFICE:                       20800 Swenson Drive
                                                     Suite 350
                                                     Waukesha, WI 53186

5.       HELLER BUSINESS CREDIT
         150 East 42nd Street, 7th Floor
         New York, NY 10017

         COMMITMENT AMOUNT:                          $25,000,000

         DOMESTIC LENDING OFFICE:           150 East 42nd Street, 7th Floor
                                                     New York, NY 10017

         LIBOR LENDING OFFICE:                       150 East 42nd Street,
                                                     7th Floor
                                                     New York, NY 10017

6.       IBJ WHITEHALL BUSINESS CREDIT
         One State Street, 6th Floor
         New York, NY 10004

         COMMITMENT AMOUNT:                          $15,000,000

         DOMESTIC LENDING OFFICE:           One State Street, 6th Floor
                                                     New York, NY 10004
         LIBOR LENDING OFFICE:                       One State Street, 6th Floor
                                                     New York, NY 10004




<PAGE>   22


7.       LASALLE BANK NATIONAL ASSOCIATION
         135 South LaSalle Street
         Suite 305 SE
         Chicago, IL 60603

         COMMITMENT AMOUNT:                          $31,665,000

         DOMESTIC LENDING OFFICE:           135 South LaSalle Street
                                                     Suite 305 SE
                                                     Chicago, IL 60603

         LIBOR LENDING OFFICE:                       135 South LaSalle Street
                                                     Suite 305 SE
                                                     Chicago, IL 60603

8.       NATIONAL BANK OF CANADA
         225 West Washington Street
         Suite 1100
         Chicago, IL 60606

         COMMITMENT AMOUNT:                          $15,000,000

         DOMESTIC LENDING OFFICE:           225 West Washington Street
                                                     Suite 1100
                                                     Chicago, IL 60606

         LIBOR LENDING OFFICE:                       225 West Washington Street
                                                     Suite 1100
                                                     Chicago, IL 60606

9.       PNC BUSINESS CREDIT
         Two PNC Plaza, 18th Floor
         620 Liberty Avenue
         Pittsburgh, PA 15222

         COMMITMENT AMOUNT:                          $20,000,000

         DOMESTIC LENDING OFFICE:           Two PNC Plaza, 18th Floor
                                                     620 Liberty Avenue
                                                     Pittsburgh, PA 15222

         LIBOR LENDING OFFICE:                       Two PNC Plaza, 18th Floor
                                                     620 Liberty Avenue
                                                     Pittsburgh, PA 15222



<PAGE>   23


EXHIBIT C
TO
AMENDMENT NO.7
DATED AS OF MAY 31, 2000

AMENDED SCHEDULE S TO CREDIT AGREEMENT

ATTACHED.