Document:

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                                                                     EXHIBIT 4.1

                              BIOVEST [AND DESIGN]

  NUMBER                                                            SHARES
    B1

                           BIOVEST INTERNATIONAL, INC.

INCORPORATED UNDER THE LAWS                                      SEE REVERSE FOR
 OF THE STATE OF DELAWARE                                          DEFINITIONS

THIS IS TO CERTIFY THAT                                        CUSIP 09069L 10 2

                                 IS THE OWNER OF

     FULLY PAID AND NON-ASSESSABLE SHARES OF COMMON STOCK OF THE PAR VALUE OF
                 $0.01 PER SHARE OF BIOVEST INTERNATIONAL, INC.

transferable on the books of the Corporation by the holder hereof in person or
by duly authorized attorney upon surrender of this Certificate properly
endorsed. This Certificate is not valid unless countersigned by the Transfer
Agent and Registrar.

WITNESS the facsimile seal of the Corporation and the facsimile signature of its
duly authorized officers.

Dated:

     President    [Corporate Seal]    Chairman and Chief Executive Officer

This Corporation will furnish without charge to each stockholder who so requests
a statement of the designations, relative rights, preferences, and limitations
applicable to each class of shares and the variations in rights, preferences,
and limitations determined for each series therof (and the authority of the
Board of Directors to determine variations for future series). Such request may
be addressed to the secretary of the Corporation or to the transfer agent and
registrar named on the face of this certificate.

The following abbreviations, when used in the inscription on the face of this
certificate, shall be construed as though they were written out in full
according to applicable laws or regulations.

TEN COM - as tenants in common
TEN ENT - as tenants by the entireties
JT  TEN - as joint tenants with right of
            survivorship and not as tenants in common

UNIF GIFT MIN ACT - ______________ Custodian _____________________
                        (Cust)                      (Minor)

Under Uniform Gifts to Minors Act

__________________________________________
(State)

     Additional abbreviations may also be used though not in the above list.

For Value Received, ______________ hereby sell, assign and transfer unto

PLEASE INSERT SOCIAL SECURITY OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE

 ____________________________________
|____________________________________|________________________________________

______________________________________________________________________________
(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE, OF
 ASSIGNEE)
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
_____________________________________________________________________ shares

of the capital stock represented by the within Certificate, and do hereby
irrevocably constitute and appoint____________________________________________
______________________________________________________________________________
______________________________________________________________________________

Attorney to transfer the said stock on the books of the within-named
Corporation, with full power of substitution in the premises.

Dated _______________________

                     NOTICE:
             THE SIGNATURE(S) TO      X ______________________________________
             THE ASSIGNMENT MUST                     (Signature)
             CORRESPOND WITH THE
             NAME(S) AS WRITTEN
             UPON THE FACE OF THE
             CERTIFICATE IN EVERY
             PARTICULAR WITHOUT
             ALTERATION OR            X ______________________________________
             ENLARGEMENT OR ANY                      (Signature)
             CHANGE WHATSOEVER

                               _______________________________________________
                                 THE SIGNATURE(S) MUST BE GUARANTEED BY AN
                                 ELIGIBLE GUARANTOR INSTITUTION (BANKS,
                                 STOCKBROKERS, SAVINGS AND LOAN
                                 ASSOCIATIONS AND CREDIT UNIONS WITH
                                 MEMBERSHIP IN AN APPROVED SIGNATURE
                                 GUARANTEE MEDALLION PROGRAM), PURSUANT TO
                                 S.E.C. RULE 17Ad-15.
                               _______________________________________________
                                 SIGNATURE(S) GUARANTEED BY:<PAGE>

                                                                   EXHIBIT 10.1b

                       FIRST AMENDMENT TO CREDIT AGREEMENT

This Amendment is made effective as of the 31st day of August, 2000, by and
between HEI, Inc., a Minnesota corporation (the "Borrower"), and LaSalle
Business Credit, Inc., a Delaware corporation (the "Lender").

                                    Recitals

The Borrower and the Lender have entered into that certain Loan and Security
Agreement dated as of July 31, 2000 (the "Loan Agreement").

The Borrower may request certain advances from the Lender from time to time
pursuant to the Loan Agreement, and the Lender has agreed to make capital
expenditure loans, and to make available letters of credit, to or for the
benefit of the Borrower pursuant to the terms of the Loan Agreement.

The revolving loan advances under the Loan Agreement are evidenced by the
Borrower's revolving note dated July 31, 2000, in the maximum principal amount
of $5,000,000 and payable to the order of the Lender (the "Revolving Note"). The
capital expenditure loan made under the Loan Agreement to date is evidenced by
the Borrower's capital expenditure note dated July 31, 2000, in the original
principal amount of $1,665,000 (the "Capex Note").

All indebtedness of the Borrower to the Lender is secured pursuant to the terms
of the Loan Agreement and all Other Agreements as defined therein (collectively,
the "Security Documents").

NOW, THEREFORE, in consideration of the premises and of the mutual covenants and
agreements herein contained, it is agreed as follows:

1. Terms used in this Amendment which are defined in the Loan Agreement shall
have the same meanings as defined therein, unless otherwise defined herein.

2. The Loan Agreement is hereby amended as follows:

     (a) Section 1 of the Loan Agreement is hereby amended by adding to said
     Section the following definitions:

          "EXHIBIT D" shall mean the exhibit entitled Exhibit D - Form of Term
     Note, which is attached hereto and made a part hereof.

          "REMARKETING AGREEMENT" shall mean that certain Remarketing Agreement
     dated as of November __, 2000 by and between the Borrower and LaSalle
     Capital Markets, a division of ABN AMRO Financial Services, Inc., as
     remarketing agent.

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          "TERM LOANS" shall have the meaning specified in paragraph 3.A.
     hereof.

          "TERM NOTE" shall mean, collectively or individually, as the context
     requires, the term notes in the maximum aggregate original principal amount
     of $3,200,000, which may be executed by Borrower to the order of LaSalle
     from time to time in accordance with paragraph 3.A. hereof, in the form
     attached hereto as Exhibit D.

     (b) Section 1of the Loan Agreement is hereby further amended by deleting
     the definitions of "Kind", "Loan" or "Loans", "Note" and "Prime Rate Loan"
     from said Section and replacing the same with the following:

          "KIND" shall mean, with respect to any Loan, whether such Loan is a
     Revolving Loan, a Capex Loan or a Term Loan.

          "LOAN" or "LOANS" shall mean any and all Revolving Loans, Capex Loans
     and Term Loans made by LaSalle to Borrower pursuant to paragraphs 2, 3 and
     3.A. hereof and all other loans, advances and financial accommodations made
     by LaSalle to or on behalf of Borrower hereunder.

          "NOTE" shall mean the Revolving Note, the Capex Note or the Term Note.

          "PRIME RATE LOAN" shall mean a Revolving Loan, a Term Loan or the
     portion of the Capex Loan that bears interest based on the Prime Rate.

     (c) The Loan Agreement is hereby amended by adding thereto a new Section
     3.A., reading as follows:

          "3.A. TERM LOANS

     LaSalle shall make non-revolving loans and advances (collectively, the
     "Term Loan") to Borrower as may from time to time be requested or deemed to
     be requested, in an aggregate amount of up to but not exceeding Three
     Million Two Hundred Thousand and 00/100 ($3,200,000.00), in accordance with
     the terms of this paragraph 3.A. Term Loan advances shall be made hereunder
     only if and to the extent that (i) Bonds have been tendered pursuant to the
     Mandatory Tender or an Optional Tender, (ii) all or a portion of such
     tendered Bonds have not been remarketed pursuant to the Remarketing
     Agreement, and (iii) funds are drawn on the Victoria Letter of Credit as a
     result of the failure to remarket the Bonds (collectively, the "Term Loan
     Conditions"). Borrower shall execute and deliver to LaSalle a Term Note at
     the time each Term Loan is advanced to or for the benefit of Borrower
     hereunder. Principal payable on account of each Term Loan shall be payable
     in successive monthly installments (i) payable on the first day of each
     month, the first of which installments shall be due and payable on the

                                      -2-

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     first day of the month immediately following the date of each Term Note and
     (ii) based on an amortization schedule consisting of thirty-six (36) equal
     and level payments under each Term Note; provided, however, that the entire
     unpaid principal balance of each Term Loan shall be due and payable in full
     upon the earlier of (A) expiration of the Original Term of this Agreement,
     or (B) the date which is thirteen (13) months after the date of each
     corresponding Term Note; and, provided further, that the amount of each
     monthly installment of principal payable in respect of the Term Loan shall
     in no event be greater than $58,333.33. Notwithstanding anything
     hereinabove to the contrary, the entire unpaid principal balance of the
     Term Loan, and any accrued and unpaid interest thereon, shall be
     immediately due and payable upon the earlier to occur of (i) the last day
     of the Original Term or the last day of any Renewal Term, if either LaSalle
     or Borrower elects to terminate this Agreement as of the end of any such
     Original or Renewal Term and (ii) the acceleration of the Liabilities
     pursuant to paragraph 17 of this Agreement."

     (d) Section 5(a) of the Loan Agreement is hereby amended by (i) adding a
     new fourth sentence to said Section, reading as follows: "Except as
     otherwise provided in paragraph 6 (c), interest shall accrue on the unpaid
     principal balance of the Term Loan made to the Borrower at a fluctuating
     rate per annum equal to four percent (4.0%) above the Prime Rate."; and
     (ii) adding the following language to the end of said Section: "and (3)
     with respect to Term Loans, the rate of interest then in effect under
     paragraph 5, plus two percent (2.0%)".

     (e) Section 6 (a) of the Loan Agreement is hereby amended by (i) adding the
     phrase "and for a Term Loan" to the first line thereof following the phrase
     "for a Capex Loan", and (ii) adding the following language to the end of
     the first sentence thereof: "; and (iii) the occurrence of the Term Loan
     Conditions shall be deemed irrevocably to be a request for a Term Loan on
     the date of such occurrence in the amount of the draw under the Victoria
     Letter of Credit made in connection with such occurrence."

     (f) Section 6 (b) of the Loan Agreement is hereby amended by (i) adding the
     phrase "and each Term Loan" to the second line thereof following the phrase
     "and each Capex Loan", and (ii) adding the language "and each Term Loan
     requested under paragraph 6(a)(iii)" following the phrase "under paragraph
     6(a)(ii)".

     (g) Section 15 of the Loan Agreement is hereby amended by deleting the term
     "Term Loan" as set forth in the first line of subsection (a) thereof and in
     the second line of subsection (a)(iv) thereof and replacing the same with
     the term "Capex Loan".

     (h) The Loan Agreement is hereby amended by attaching thereto as Exhibit D
     the form of Term Note attached hereto as Exhibit D.

                                      -3-

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3. Except as explicitly amended by this Amendment, all of the terms and
conditions of the Loan Agreement shall remain in full force and effect and shall
apply to any advance thereunder.

4. This Amendment shall be effective as of August 31, 2000, upon receipt by the
Lender of (i) an executed original hereof, together with the acknowledgement and
agreement of guarantor set forth at the end of this Amendment, executed by the
Corporate Guarantor, and (ii) a fully-earned, non-refundable accommodation fee
in the amount of $10,000.

5. The Borrower hereby represents and warrants to the Lender as follows:

     (a) The Borrower has requisite power and authority to execute this
     Amendment and to perform all of its obligations hereunder, and this
     Amendment has been duly executed and delivered by the Borrower and
     constitutes the legal, valid and binding obligation of the Borrower,
     enforceable in accordance with its terms.

     (b) The execution, delivery and performance by the Borrower of this
     Amendment have been duly authorized by all necessary corporate action and
     do not (i) require any authorization, consent or approval by any
     governmental department, commission, board, bureau, agency or
     instrumentality, domestic or foreign, (ii) violate any provision of any
     law, rule or regulation or of any order, writ, injunction or decree
     presently in effect, having applicability to the Borrower, or the articles
     of incorporation or by-laws of the Borrower, or (iii) result in a breach of
     or constitute a default under any indenture or loan or credit agreement or
     any other agreement, lease or instrument to which the Borrower is a party
     or by which it or its properties may be bound or affected.

     (c) All of the representations and warranties contained in Article V of the
     Loan Agreement are correct on and as of the date hereof as though made on
     and as of such date, except to the extent that such representations and
     warranties relate solely to an earlier date.

6. All references in the Loan Agreement to "this Agreement" shall be deemed to
refer to the Loan Agreement as amended hereby; and any and all references in the
Security Documents to the Loan Agreement shall be deemed to refer to the Loan
Agreement as amended hereby.

7. The execution of this Amendment and any documents related hereto shall not be
deemed to be a waiver of any Default or Event of Default under the Loan
Agreement or breach, default or event of default under any Security Document or
other document held by the Lender, whether or not known to the Lender and
whether or not existing on the date of this Amendment.

8. The Borrower hereby absolutely and unconditionally releases and forever
discharges the Lender, and any and all participants, parent corporations,
subsidiary corporations, affiliated corporations, insurers, indemnitors,
successors and assigns thereof, together with all of the present and former
directors, officers, agents and employees of any of the foregoing, from any and
all claims, demands or causes of action of any kind, nature or description,
whether arising in law or equity or upon contract or tort or under any state or

                                      -4-

<PAGE>

federal law or otherwise, which the Borrower has had, now has or has made claim
to have against any such person for or by reason of any act, omission, matter,
cause or thing whatsoever arising from the beginning of time to and including
the date of this Amendment, whether such claims, demands and causes of action
are matured or unmatured or known or unknown.

9. The Borrower hereby reaffirms its agreement under the Loan Agreement to pay
or reimburse the Lender on demand for all costs and expenses incurred by the
Lender in connection with the Loan Agreement, the Security Documents and all
other documents contemplated thereby, including without limitation all
reasonable fees and disbursements of legal counsel. Without limiting the
generality of the foregoing, the Borrower specifically agrees to pay all fees
and disbursements of counsel to the Lender, in an amount up to $2,000, for the
services performed by such counsel in connection with the preparation of this
Amendment and the documents and instruments incidental hereto. The Borrower
hereby agrees that the Lender may, at any time or from time to time in its sole
discretion and without further authorization by the Borrower, make a loan to the
Borrower under the Loan Agreement, or apply the proceeds of any loan, for the
purpose of paying any such fees, disbursements, costs and expenses and the fee
required under paragraph 4 hereof.

10. This Amendment may be executed in any number of counterparts, each of which
when so executed and delivered shall be deemed an original and all of which
counterparts, taken together, shall constitute one and the same instrument.

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

                                       HEI, INC.

                                       By: _____________________________________

                                           Its: ________________________________

                                       LASALLE BUSINESS CREDIT, INC.

                                       By: _____________________________________

                                           Its: ________________________________

                                      -5-

<PAGE>

                    ACKNOWLEDGMENT AND AGREEMENT OF GUARANTOR

     The undersigned, a guarantor of the indebtedness of HEI, Inc. (the
"Borrower") to LaSalle Business Credit, Inc. (the "Lender") pursuant to a
Continuing Unconditional Guaranty dated as of July 31, 2000 (the "Guaranty"),
hereby (i) acknowledges receipt of the foregoing Amendment; (ii) consents to the
terms (including without limitation the release set forth in paragraph 8 of the
Amendment) and execution thereof; (iii) reaffirms its obligations to the Lender
pursuant to the terms of the Guaranty; and (iv) acknowledges that the Lender may
amend, restate, extend, renew or otherwise modify the Loan Agreement and any
indebtedness or agreement of the Borrower, or enter into any agreement or extend
additional or other credit accommodations, with such notice to or consent of the
undersigned as may be expressly required pursuant to the terms of the Guaranty
for all of the Borrower's present and future indebtedness to the Lender.

                                       CROSS TECHNOLOGY, INC.

                                       By:______________________________________

                                          Its: _________________________________

                                      -6-

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