Document:

<PAGE>

                                                                   Exhibit 10.1

                                   [Letterhead]

Biomagnetic Technologies, Inc.
Attn: Mr. Aron Stern, CEO
9727 Pacific Heights Blvd.
San Diego, CA 92121 3719

Zurich, December 21, 1999
(kred/ESGA/verach/Biomagnetic)

LOAN AGREEMENT NR ***

Dear Sirs,

With reference to our various discussions, we are pleased to make available
to you a loan facility on the following terms and conditions (hereinafter
referred to as the "Agreement"):

BORROWER

Biomagnetic Technologies, Inc., 9727 Pacific Heights Blvd., San Diego, CA
92121 3719
(hereinafter referred to as the "Borrower")

LENDER

AIG Private Bank Ltd., ***
(hereinafter referred to as the "Lender")

LOAN AMOUNT

USD 11'000'000.00 (United States Dollars eleven million)

PURPOSE

For the purchase of all outstanding shares of Neuromag Oy, Helsinki from
Picker International Inc., Cleveland.

*** Portions of this page have been omitted pursuant to a request for
    confidential treatment filed separately with the Commission.

<PAGE>

Loan Agreement, dated December 21, 1999                                   Page 2
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UTILISATION

In the form of fixed terms ("Advance(s)") in US Dollars with interest periods
of 1 to 6 months, no Advance to exceed the term of this Agreement, and in
minimum amounts of USD 2 million. The aggregate amount of all fixed term
advances outstanding shall not exceed the total amount of the loan facility.

PAYOUT

As per separate written drawdown instructions, which must be received by the
Lender at least 3 (three) Business days prior to payout, subject to the
satisfaction of all conditions precedent.

TERM / DURATION

This credit facility will be available until June 30, 2000 (the "Final
Maturity Date").

REPAYMENT

The Borrower shall repay in full all outstanding advances made to it on the
Final Maturity Date, or before at his discretion, on any roll-over date.

INTEREST RATE

The Borrower agrees to pay interest on all principal amounts outstanding in
accordance with the following provisions:

The interest rate for fixed term advances shall be the rate per annum which
is the sum of the margin of 3.5% (three and a half per cent) per annum and
the rate at which deposits in US Dollars for the relevant tenor and amount
are offered by the Lender to prime banks in the London interbank market two
business days prior to the beginning of an interest period.

Interest will be calculated on the basis of the exact number of days elapsed,
divided by a 360-day year (365/360) and will be payable at the end of each
interest period.

If any sum due and payable by the Borrower is not paid when due, the interest
on any such amounts will be calculated on the basis of the refinancing costs
of the Lender, together with the margin of *** (*** per cent) per annum, for
the period beginning with the due date until receipt by the Lender of the
payment.

*** Portions of this page have been omitted pursuant to a request for
    confidential treatment filed separately with the Commission.

<PAGE>

Loan Agreement, dated December 21, 1999                                   Page 3
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If any payment date shall fall on a day on which banks in Zurich or New York
are not open for business, such payment date shall be extended to the next
succeeding business day unless such business day falls in the next calendar
month in which event such due date shall be the immediately preceeding
business day.

SECURITY

1.  Pledge and assignment with the enclosed form "General Deed of Pledge and
    Declaration of Assignment" of all outstanding shares in Neuromag Oy,
    Helsinki, to be deposited with the Lender.

2.  Pledge and assignment by Scaloway Co. Ltd. (hereinafter referred to as
    "Guarantor") in a form acceptable to the Lender of a time deposit in the
    amount of USD ***--(United States Dollars ***).

ESTABLISHMENT FEE

The Borrower shall pay to the Lender an Establishment Fee of USD 20'000. --
flat of the Loan Amount, due upon signing of this Agreement. At the Lender's
discretion, this fee may be either paid immediately or deducted upon
disbursement.

COSTS, FEES AND EXPENSES

The Borrower shall pay to the Lender on demand an amount equal to all costs,
charges and expenses (including, but not limited to, legal expenses and stamp
registration or other duties) incurred by the Lender in connection with
preparation and execution of this Agreement and the security and other
documentation contemplated hereby and all costs, charges and expenses
(including legal expenses on a full indemnity basis) of the Lender in
connection with the enforcement of or preservation of any of its rights under
this Agreement or otherwise in connection with the facility.

PREPAYMENT

The Borrower may at any time, upon prior written notice of 3 days to the
Lender, prepay a portion of or the entire amount outstanding, as of the end
of any interest period. Amounts prepaid may not be reborrowed.

*** Portions of this page have been omitted pursuant to a request for
    confidential treatment filed separately with the Commission.

<PAGE>

Loan Agreement, dated December 21, 1999                                   Page 4
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PAYMENTS AND TAXES

All payments to be made by the Borrower to the Lender under this Agreement
shall be made in United States Dollars, freely disposable outside of
bilateral or multilateral payment agreements which may exist at the time of
payment, free and clear of and without deduction of any taxes, levies,
imposts, duties, charges, fees, deductions or withholdings of any nature, now
or hereafter imposed by or on behalf of any taxing authority or any other
entity.

ASSIGNABILITY

The Lender has the right to assign this Agreement to any party without the
consent of the Borrower but it requires the consent of the Guarantor.

COVENANTS

The Borrower covenants that, until full and final payment of all indebtedness
and liabilities incurred hereunder, unless the Lender waives compliance in
writing, the Borrower will furnish the Lender with such information
concerning the affairs of the Borrower as the Lender may reasonably request.

EVENTS OF DEFAULT

The principal and accrued interest on any outstanding balances as well as
any and all accrued fees and charges whatsoever under this Agreement, shall
become immediately due and payable, without need of further legal formality,
at the option of and upon the first demand by the Lender, if:

a)  the Borrower shall default in the payment of principal or interest on any
    advance or of any other amount payable thereunder when the same shall become
    due and payable and such failure continues for a period of 5 (five) business
    days without remedy;
b)  the Borrower shall default in the performance of any term, covenant or
    condition contained in this agreement after written notice and failure to
    cure such default within thirty (30) days from the receipt of such notice
    or an event of default in the performance of any other agreement between
    the Borrower and the Lender;
c)  any representation or warranty made by the Borrower under this agreement
    or any certificate or documents furnished pursuant thereto, shall prove to
    have been untrue when made or at any subsequent time to be incorrect in any
    material respect;
d)  any other event occurs or circumstances arise which, in the opinion of
    the Lender is likely, materially and adversely, to affect the ability of
    the Borrower or any future mortgagor to perform all or any of his or its
    obligations under or otherwise to comply with the terms of this Agreement.

The Borrower shall hold the Lender harmless of and indemnify the Lender
against any losses or expenses which the Lender may sustain or incur as a
consequence of any Event of Default by the Borrower as stipulated herein.

<PAGE>

Loan Agreement, dated December 21, 1999                                   Page 5
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If there is an Event of Default, the Lender reserves the right to increase the
interest rate and/or the commission rate, not to exceed *** percent per annum.

CONDITIONS PRECEDENT

This agreement its made under the condition and the Lender's obligation to
make this loan available is subject to the conditions precedent that the
Lender shall have received and approved the following:

a)  A signed copy of this agreement, each page initialed, bearing the
    authorized signature of the Borrower.

b)  Proper and completed assignment of all the collateral as per cif. 2 of the
    Security paragraph.

LAW GOVERNING THE LEGAL RELATIONSHIP BETWEEN THE LENDER AND THE BORROWER AND
PLACE OF JURISDICTION

All legal aspects of the relationship between the Borrower and the Lender
shall be governed by Swiss law. The place of performance, the exclusive place
of jurisdiction for lawsuits and all other kinds of legal proceedings and
place of foreclosure shall be the domicile of the Lender.

The Lender reserves the right to bring legal proceedings against the Borrower
before any competent court at the domicile of the Borrower or any other court
having jurisdiction over the Borrower.

No failure to exercise and no delay in exercising on the part of the Lender
any of its rights hereunder shall operate as a waiver thereof, nor shall any
single or partial exercise or any rights preclude any other or further
exercise thereof.

The general pledge and assignment and our "General Banking Conditions" which
you already received, form an integral part of this loan agreement.

We hope that the above terms and conditions meet your requirements, and
kindly request that you duly sign and return to us the enclosed duplicates of
this agreement together with all other required documents.

*** Portions of this page have been omitted pursuant to a request for
    confidential treatment filed separately with the Commission.

<PAGE>

Loan Agreement, dated December 21, 1999                                   Page 6
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We look forward to hearing from you and remain

Yours truly,

AIG Private Bank Ltd.

/s/ Esther Gauch              /s/ Werner Vontobel
----------------              -------------------
  Esther Gauch                  Werner VontobelPrepared by MERRILL CORPORATION www.edgaradvantage.com

Exhibit 4(a)

    AMENDMENT
No. 5 entered into as of January 12, 2000 (this "Amendment"), to the Credit Agreement dated as of February 12, 1998
(as amended, supplemented or otherwise modified from time to time, the "Credit Agreement"), among Magellan Health Services, Inc., a Delaware
corporation (the "Parent Borrower"); Charter Behavioral Health System of New Mexico, Inc., a New Mexico corporation; Merit Behavioral Care Corporation,
a Delaware corporation; each other wholly owned domestic subsidiary of the Parent Borrower that becomes a "Subsidiary Borrower" pursuant to
Section 2.23 of the Credit Agreement (each, a "Subsidiary Borrower" and, collectively, the "Subsidiary
Borrowers" (such term is used herein as modified in Article I of the Credit Agreement); the Parent Borrower and the Subsidiary Borrowers are collectively referred to herein as
the "Borrowers"); the Lenders (as defined in Article I of the Credit Agreement); The Chase Manhattan Bank, a New York banking corporation, as
administrative agent (in such capacity, the "Administrative Agent") for the Lenders, as collateral agent (in such capacity, the
"Collateral Agent") for the Lenders and as an issuing bank (in such capacity, an "Issuing Bank"); First
Union National Bank, a national banking corporation, as syndication agent (in such capacity, the "Syndication Agent") for the Lenders and as an issuing
bank (in such capacity, an "Issuing Bank"); and Credit Lyonnais New York Branch, a licensed branch of a bank organized and existing under the laws of
the Republic of France, as documentation agent (in such capacity, the "Documentation Agent") for the Lenders and as an issuing bank (in such capacity,
an "Issuing Bank" and, together with The Chase Manhattan Bank and First Union National Bank, each in its capacity as an issuing bank, the
"Issuing Banks").

    A.  The
Lenders and the Issuing Banks have extended credit to the Borrowers, and have agreed to extend credit to the Borrowers, in each case pursuant to the terms and
subject to the conditions set forth in the Credit Agreement.

    B.  The
Parent Borrower has requested that the Required Lenders amend certain provisions of the Credit Agreement as set forth herein, and the Required Lenders are
willing so to amend such provisions of the Credit Agreement, on the terms and subject to the conditions set forth in this Amendment.

    C.  Capitalized
terms used but not defined herein have the meanings assigned to them in the Credit Agreement (as amended hereby).

    Accordingly,
in consideration of the mutual agreements herein contained and other good and valuable consideration, the sufficiency and receipt of which are hereby acknowledged, the
parties hereto agree as follows:

    SECTION
1.  Amendments to Section 1.01. (a)  The definition of the term "Acquired Entity EBITDA" in
Section 1.01 of the Credit Agreement is hereby amended by adding the following new sentence at the end of the existing definition:

If
the portion of the Acquired Entity EBITDA of any Acquired Entity for any period ending (a) within one year following the date of acquisition of such Acquired Entity and (b) on or prior to March 31,
2001, that is attributable to the portion of such period ending on such date of acquisition is negative, then, if elected by the Parent Borrower, such portion of such Acquired Entity EBITDA shall be
deemed to be zero, provided that, during the term of this Agreement, the aggregate amount of all Acquired Entity EBITDA deemed to be zero pursuant to
such an election by the Parent Borrower shall not exceed $7,500,000.

    (b) The
definition of the term "Consolidated Current Assets" in Section 1.01 of the Credit Agreement is hereby amended by deleting the existing definition and replacing
it in its entirety as follows:

"Consolidated Current Assets" shall mean, at any date of determination, all assets (excluding cash and cash-equivalents, other than cash and
cash-equivalents held in any escrow or special purpose or

restricted account to the extent that such cash and cash-equivalents relate to liabilities comprising "medical claims payable" or other current liabilities related to such "medical claims
payable", in any case, to the extent the same are included in Consolidated Current Liabilities) that would, in accordance with GAAP, be classified on a consolidated balance sheet of the Parent
Borrower and the Subsidiaries as current assets at such date of determination.

    (c) The
definition of the term "Consolidated Net Worth" in Section 1.01 of the Credit Agreement is hereby amended by deleting the existing definition and replacing it
in its entirety as follows:

"Consolidated Net Worth" shall mean, as at any date of determination, the sum of (a) the consolidated stockholders' equity of the Parent Borrower
and the Subsidiaries, as determined on a consolidated basis in accordance with GAAP, and (b) to the extent not reflected in the calculation in clause (a) above, the Net Cash Proceeds of
each Equity Issuance.

    (d) The
definition of the term "Permitted Non-Guarantor Transactions" is amended by replacing each reference to "$25,000,000" in that definition with a
reference to "$35,000,000".

    (e) The
definition of the term "Permitted Non-Control Investments" is amended by replacing each reference to "$25,000,000" in that definition with a
reference to "$35,000,000".

    (f) The
definition of the term "Specified Equity Issuance" is amended by (i) inserting after the text "March 31, 2000" the text:

(or,
in the case of an Equity Issuance made upon the exercise of any option granted by the Parent Borrower, the terms and conditions of which option have been approved by the Required Lenders, on or
before the last date that such option may be exercised under such terms and conditions (as in effect on the date of such approval by the Required Lenders))

    (ii) replacing
the reference to "$76,000,000" in that definition with a reference to "$85,000,000".

    SECTION
2.  Amendment to Section 5.04(c).  Section 5.04(c) is amended and restated in its entirety to
read:

(c)
within (i) 30 days after the end of each month (other than (A) the last month of any fiscal quarter and (B) the month of October), and (ii) within 45 days after the end of each October, its
unaudited consolidated balance sheet and related statements of income and cash flows, showing the consolidated financial condition of the Parent Borrower and its consolidated Subsidiaries, in all
cases as of the close of such month, and the consolidated results of its operations and cash flows during such month and the then-elapsed portion of the fiscal year.

    SECTION
3.  Approval of Option Issuance and Exercise.  By its execution hereof, each Lender shall have
given its approval to (a) the terms and conditions of the option to acquire Capital Stock of the Parent Borrower described in the letter (the "Request
Letter") from the Parent Borrower to the Administrative Agent dated December 22, 1999 (including all attachments thereto), and (b) to the terms of any
Specified Equity Issuance that would result from the exercise of such option in accordance with such terms and conditions.

    SECTION
4.  Limited Waiver of Section 6.06.  The Required Lenders hereby waive compliance by the
Borrowers and the Subsidiaries with the provisions of Section 6.06(a) to the Credit Agreement to the extent, but only to the extent, necessary to permit the Parent Borrower to repurchase (the
"Rainwater Repurchase") shares of its Series A Preferred Stock from TPG Magellan, LLC and certain of its affiliates and assignees (collectively,
"TPG Magellan"), provided that (a) the Rainwater Repurchase is consummated pursuant to the exercise by
Rainwater-Magellan Holdings, L.P. and its affiliates and assignees (collectively, "Rainwater") of certain pre-emptive rights described under
the heading "Pre-Emptive Rights" in the attachment to the Request Letter and (b) substantially simultaneously with the Rainwater Repurchase,
(i) an equivalent number of shares of Series A Preferred Stock of the Parent Borrower is issued to Rainwater

and (ii) the Parent Borrower receives aggregate cash consideration from Rainwater equivalent to the aggregate cash consideration paid by the Parent Borrower to TPG Magellan in connection with the
Rainwater Repurchase.

    SECTION
5.  Representations and Warranties.  Each Borrower represents and warrants to the Administrative
Agent and to each of the Lenders that:

    (a) This
Amendment has been duly authorized, executed and delivered by it and constitutes a legal, valid and binding obligation of each Loan Party hereto, enforceable
against such Loan Party in accordance with its terms.

    (b) Before
and after giving effect to this Amendment, the representations and warranties set forth in Article III of the Credit Agreement are true and correct in all
material respects on and as of the date hereof with the same effect as if made on and as of the date hereof, except to the extent such representations and warranties expressly relate to an earlier
date.

    (c) Before
and after giving effect to this Amendment, no Event of Default or Default has occurred and is continuing.

    SECTION
6.  Amendment Fee.  In consideration of the agreements of the Lenders contained in this
Amendment, the Parent Borrower agrees to pay to the Administrative Agent, for the account of each Lender that delivers an executed counterpart of this Amendment prior to 3:00 p.m., New York City time,
on January 12, 2000, an amendment fee (the "Amendment Fee") in an amount equal to 0.05% of the sum of such Lender's outstanding Term Loans and Revolving
Credit Commitment as of such date.

    SECTION
7.  Conditions to Effectiveness.  This Amendment shall become effective as of December 31,
1999, when (a) the Administrative Agent shall have received (i) counterparts of this Amendment that, when taken together, bear the signatures of the Borrowers and the Required Lenders and (ii) the
Amendment Fees, (b) the representations and warranties set forth in Section 5 hereof are true and correct and (c) all fees and expenses required to be paid or reimbursed by the Borrowers pursuant
hereto or to the Credit Agreement shall have been paid or reimbursed, as applicable.

    SECTION
8.  Credit Agreement.  Except as specifically amended hereby, the Credit Agreement shall continue
in full force and effect in accordance with the provisions thereof as in existence on the date hereof. After the date hereof, any reference to the Credit Agreement shall mean the Credit Agreement as
amended hereby. This Amendment shall be a Loan Document for all purposes.

    SECTION
9.  Applicable Law.  THIS AMENDMENT SHALL BE
GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

    SECTION
10.  Counterparts.  This Amendment may be executed in two or more counterparts, each of which
shall constitute an original but all of which when taken together shall constitute but one agreement. Delivery of an executed signature page to this Amendment by facsimile transmission shall be
effective as delivery of a manually signed counterpart of this Amendment.

    SECTION
11.  Expenses.  The Parent Borrower agrees to reimburse the Administrative Agent for its
out-of-pocket expenses in connection with this Amendment, including the reasonable fees, charges and disbursements of Cravath, Swaine & Moore, counsel for the Administrative
Agent.

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

	 	 	MAGELLAN HEALTH SERVICES, INC.,
	 

 	 
 	 

by	 
 	 

/s/ JAMES R. BEDENBAUGH   
	 	 	 	 	
 Name: James R. Bedenbaugh

Title:  Senior Vice President & Tresurer
	 

 	 
 	 

CHARTER BEHAVIORAL HEALTH SYSTEM OF NEW MEXICO, INC.,
	 

 	 
 	 

by	 
 	 

/s/ CHARLOTTE A. SANFORD   
	 	 	 	 	
 Name: Charlotte A. Sanford

Title:  Treasurer
	 

 	 
 	 

MERIT BEHAVIORAL CARE CORPORATION,
	 

 	 
 	 

by	 
 	 

/s/ CHARLOTTE A. SANFORD   
	 	 	 	 	
 Name: Charlotte A. Sanford

Title:  Treasurer
	 

 	 
 	 

THE CHASE MANHATTAN BANK, individually and as Administrative Agent, Collateral Agent and an Issuing Bank,
	 

 	 
 	 

by	 
 	 

/s/ DAWN LEE LUM   
	 	 	 	 	
 Name: Dawn Lee Lum

Title:  Vice President
	 

 	 
 	 

FIRST UNION NATIONAL BANK, individually and as Syndication Agent and an Issuing Bank,
	 

 	 
 	 

by	 
 	 

/s/ JOYCE C. BARRY   
	 	 	 	 	
 Name: Joyce C. Barry

Title:  Senior Vice President
	 

 	 
 	 

CREDIT LYONNAIS NEW YORK BRANCH, individually and as Documentation Agent and an Issuing Bank,
	 

 	 
 	 

by	 
 	 

/s/ FARBOUD TAVANGAR   
	 	 	 	 	
 Name: Farboud Tavangar

Title:  Senior Vice President

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