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                                                                     EXHIBIT 4.5

                 FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED
                            LOAN AND AGENCY AGREEMENT


         THIS FOURTH AMENDMENT TO SECOND AMENDED AND RESTATED LOAN AND AGENCY
AGREEMENT (this "Amendment"), dated as of March 31, 2000, is by and among
INTERMAGNETICS GENERAL CORPORATION, a New York corporation, IGC APD CRYOGENICS
INC. (formerly known as "APD Cryogenics Inc."), a Pennsylvania corporation,
MAGSTREAM CORPORATION, a New York corporation, IGC MEDICAL ADVANCES INC.
(formerly known as "Medical Advances, Inc."), a Wisconsin corporation, INTERCOOL
ENERGY CORPORATION, a Delaware corporation, and IGC POLYCOLD SYSTEMS INC.
(formerly known as "Polycold Systems International, Inc."), a Delaware
corporation (each, a "Borrower" and collectively, the "Borrowers"), FIRST UNION
NATIONAL BANK (successor by merger to CoreStates Bank, N.A.), and THE CHASE
MANHATTAN BANK (each, a "Bank" and collectively, the "Banks").

                                   BACKGROUND

         WHEREAS, the Borrowers and the Banks are parties to a Second Amended
and Restated Loan and Agency Agreement dated October 23, 1997, as amended by
that certain First Amendment to Second Amended and Restated Loan and Agency
Agreement dated as of May 15, 1998, and as further amended by a letter agreement
dated January 28, 1999, and as further amended by a Third Amendment to Loan
Agreement dated October 15, 1999 (as at any time amended and/or extended, the
"Loan Agreement"), pursuant to which the Banks agreed to make available to the
Borrowers certain credit facilities upon the terms and conditions specified in
the Loan Agreement; and

         WHEREAS, the parties wish to amend the Loan Agreement as set forth
herein to, among other things, extend the Revolver Termination Date to October
23, 2002 and increase the Aggregate Revolving Loan Commitment from $25 million
to $27 million;

         NOW, THEREFORE, in consideration of the promises and mutual agreements
herein contained, the parties hereto, intending to be legally bound hereby,
agree to amend the Loan Agreement as herein stated.

         1. Effect of Prior Agreements. This Amendment is intended to amend the
Loan Agreement as it has been in effect to the date hereof and as it shall be
amended on and after the date hereof. All terms used herein as defined terms
shall have the meanings ascribed to them in the Loan Agreement unless herein
provided to the contrary.

         2.  Amendment. Section 2.1(a) of the Loan Agreement is hereby amended
and restated in its entirety to read as follows:

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                  "Subject to the terms and conditions hereof and in reliance
         upon the representations, warranties and covenants contained herein,
         each Bank agrees, severally and not jointly with the other Banks, to
         make revolving credit loans (collectively called the "Revolving Credit
         Loans" and each individually a "Revolving Credit Loan") to the
         Borrowers from time to time during the period commencing on the Closing
         Date and ending on October 23, 2002, or on any earlier date as provided
         in Section 2.7(b) or Section 8.1 hereof (the "Revolver Termination
         Date"), in principal amounts not to exceed at any time outstanding in
         the aggregate Twenty-Seven Million Dollars ($27,000,000) (the
         "Aggregate Revolving Loan Commitment"). For purposes of this Agreement,
         the "Revolving Loan Commitment" of First Union National Bank shall
         equal Sixteen Million Two Hundred Thousand Dollars ($16,200,000), and
         the "Revolving Loan Commitment" of The Chase Manhattan Bank shall equal
         Ten Million Eight Hundred Thousand Dollars ($10,800,000). All Loans
         shall be made by the Banks simultaneously and pro rata in accordance
         with the Revolving Loan Commitments. The failure of any one or more of
         the Banks to make Revolving Credit Loans in accordance with its or
         their obligations shall not relieve the other Banks of their several
         obligations under this Section 2.1(a), but in no event shall the
         aggregate amount at any one time outstanding which any Bank shall be
         required to lend under this Section 2.1(a) exceed the amount of such
         Bank's Revolving Loan Commitment at that time."

         3. Representations, Warranties and Covenants. Each Borrower hereby
affirms and reaffirms to the Banks all representations and warranties made and
to be made under the Loan Agreement, and confirms that all are true and correct
as of the date hereof and that no Default has occurred and is continuing. Each
Borrower further represents and warrants that it has the authority and legal
right to execute, deliver and carry out the terms of this Amendment, that such
actions were duly authorized by its Board of Directors and that the officers
executing this Amendment on its behalf were similarly authorized and empowered,
and that this Amendment does not contravene any provision of its Certificate or
Articles of Incorporation or Bylaws, or of any contract or agreement to which it
is a party or by which it or any of its properties is bound. Each Borrower
hereby affirms and reaffirms to the Banks all of the covenants contained in the
Loan Agreement including, without limitation, those contained in Articles V and
VI of the Loan Agreement and agrees to abide thereby until all of the
Obligations to the Banks are satisfied and/or discharged in their entirety.

         4. Conditions. To induce the Banks to enter into this Amendment, the
Borrowers agree as follows:

                  (a) The Borrowers shall execute and deliver to the Agent, on
behalf of the Banks, this Amendment, allonges to each of the Revolving Credit
Notes in form and substance satisfactory to the Agent, and all other documents
as the Agent may require;

                  (b) The Borrowers shall deliver to the Agent, on behalf of the
Banks, certified resolutions of the Board of Directors of each Borrower
authorizing the execution

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and delivery of the Amendment and all other documents executed in connection
herewith and therewith, all in form and substance satisfactory to the Agent; and

                  (c) Each Borrower shall deliver to the Agent a Secretary's
Certificate in form and substance satisfactory to the Agent.

         5. Further Assurances. Each Borrower hereby agrees to execute and
deliver to the Agent, on behalf of the Banks, such further agreements and other
documentation as may be requested by the Agent at any time to assure the
protection and enforcement of the Banks' rights under the Loan Agreement as
amended hereby.

         6. Reservation of Rights. To the extent any Event of Default exists on
the date hereof, any and all undertakings of any Bank under or pursuant to this
Amendment shall not be deemed a waiver by such Bank of any such Event of Default
or any of such Bank's rights and remedies under the Loan Agreement and/or
applicable law; and the Banks hereby reserve any and all such rights and
remedies.

         7. Payment of Expenses. The Borrowers shall pay to or reimburse the
Agent for, on behalf of the Banks, their respective reasonable attorneys' fees
and expenses in connection with the preparation and execution of this Amendment
and all other related documents.

         8. Reaffirmation and Extension of Agreement. Except as modified by the
terms hereof, all of the terms and conditions of the Loan Agreement and all
other Loan Documents, including, without limitation, the Notes, are hereby
affirmed and shall continue in full force and effect.

         9. Counterparts. This Amendment may be executed in two or more
counterparts, and by different parties on different counterparts, each of which
shall be deemed an original and all of which, taken together, shall constitute
one and the same instrument.

         10.Governing Law. This Amendment and the rights and obligations of the
parties hereunder shall be construed in accordance with and shall be governed by
the laws of the Commonwealth of Pennsylvania.

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

                                              INTERMAGNETICS GENERAL
                                              CORPORATION

                                              By: /s/ Michael C. Zeigler
                                                  -----------------------------
                                              Name: Michael C. Zeigler
                                              Title: CFO







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                                              IGC APD CRYOGENICS INC.

                                              By: /s/ Michael C. Zeigler
                                                  -----------------------------
                                              Name: Michael C. Zeigler
                                              Title: Treasurer

                                              MAGSTREAM CORPORATION

                                              By: /s/ Michael C. Zeigler
                                                  -----------------------------
                                              Name: Michael C. Zeigler
                                              Title: Treasurer

                                              IGC MEDICAL ADVANCES INC.

                                              By: /s/ Michael C. Zeigler
                                                  -----------------------------
                                              Name: Michael C. Zeigler
                                              Title: Treasurer

                                              INTERCOOL ENERGY CORPORATION

                                              By: /s/ Michael C. Zeigler
                                                  -----------------------------
                                              Name: Michael C. Zeigler
                                              Title: Treasurer

                                              IGC POLYCOLD SYSTEMS INC.

                                              By: /s/ Michael C. Zeigler
                                                  -----------------------------
                                              Name: Michael C. Zeigler
                                              Title: Treasurer

                                              FIRST UNION NATIONAL BANK,
                                              individually and as Agent

                                              By: /s/ Christopher Strauss
                                                  -----------------------------
                                              Name: Christopher Strauss
                                              Title:

                                              THE CHASE MANHATTAN BANK

                                              By: /s/ David C. Horan, Jr.
                                                  -----------------------------
                                              Name:  David C. Horan, Jr.
                                              Title: Vice President



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