<PAGE>   1

                                                                  EXHIBIT 10.33

Transamerica Business Credit
Technology Finance Division
76 Batterson Park Road
Farmington, CT 06032
(860) 677 6466
(860) 677-6766 Fax

January 2, 1997

Mr. John Monahan
Chief Executive Officer
Avigen, Inc.
1201 Harbor Bay Parkway, # 1000
Alameda, California 94502

Dear John:

Transamerica Business Credit Corporation - Technology Finance Division
("Lessor") is pleased to offer to lease the Equipment described below to
Avigen, Inc. ("Lessee"). This Commitment supersedes all prior correspondence,
proposals, and oral or other communications relating to leasing arrangements
between Lessee and Lessor. The outline of this offer is as follows:

Lessee:

Avigen, Inc.

Lessor:

Transamerica Business Credit Corporation - Technology Finance Division and/or
its affiliates, successors and assigns.

Guarantors:

Not Applicable.

Equipment:

A. Equipment (all equipment subject to approval of Lessor). B. Tenant
Improvements

Equipment Cost:

Type A Equipment          $1,500,000
Type B Tenant Improvements $ 500,000

Equipment Location:

Alameda, California 94502.

Anticipated Delivery:

September 1, 1996 - December 31, 1997


<PAGE>   2

Lease Term Commencement:

Upon delivery and acceptance of the Equipment or upon each completion of
deliveries and acceptance of items of Equipment with aggregate cost of not less
than $50,000, but in no event, shall any Equipment be delivered later than
December 31, 1997.

Term for Types A and B Equipment:

From each Lease Term Commencement until 36 months from the first day of the
month next following or on the same date as the Lease Term Commencement if that
date is the first date of the month.

Lease Repayment Terms for Types A and B Equipment:

Monthly Rent equal to 3.1436% of Equipment Cost shall be payable monthly in
advance. The first month's rent shall be payable upon signing the Lease and the
last month's rent shall be due upon the Lease Term Commencement. As of the date
of each Lease Term Commencement, the Monthly Rent Payments shall be fixed for
the term.

The Lessor reserves the right to increase the Monthly Rent Payments as of the
date of each Lease Term Commencement commensurate to the change in the weekly
average of the interest rates of five-year U.S. Treasury Securities from the
week ending November 11, 1996 to the week preceding the date of each Lease Term
Commencement, as published in the Wall Street Journal.

Interim Rent Payments:

In the event that the Lease Term Commencement is not on the first day of the
month, Interim Rent Payments shall accrue from each Lease Term Commencement
until the next following first day of a month and shall be payable at the end
of that month. Interim Rent Payments shall be at the daily equivalent of the
currently adjusted Monthly Rent Payment.

Purchase Option:

The Lessee shall have the option to purchase all (but not less than all) the
Equipment at the expiration of the term of the lease for the then current Fair
Market Value of the Equipment and Tenant Improvements, plus applicable sales
and other taxes.

It shall be agreed that the Fair Market Value will be equal to 10% of Equipment
and Tenant Improvements Cost.

Automatic Renewal:

In the event the Lessee does not exercise the Purchase Option described above,
the lease shall automatically renew for a term of one year with Monthly Rentals
equal to 1.5% of the original Equipment Cost and Tenant Improvement payable
monthly in advance. At the expiration of the renewal period, the Lessee shall
have the option to purchase ail (but not less than all) the Equipment and
Tenant Improvements for $1.00 plus applicable sale and other taxes.

Documentation:

The documentation relating to this transaction shall implement the transaction
contemplated by this commitment letter to the satisfaction of Lessor and Lessee
and its counsels, shall be fully acceptable





                                       65
<PAGE>   3

to Lessor and Lessee and its counsels, and shall contain conditions precedent,
representations, warranties and covenants by Lessee and shall provide for
events of defaults and remedies, all as required by Lessor and acceptable to
Lessee for transactions of this type. The documentation shall include, but not
be limited to, the terms and conditions described in this commitment letter. A
Uniform Commercial Code Fixture Filing shall be required.

Insurance:

Prior to any delivery of Equipment, the Lessee shall furnish confirmation of
insurance acceptable to the Lessor covering the Equipment and Tenant
Improvements including primary, all risk, physical damage, property damage and
bodily injury with appropriate loss payee and additional insured endorsements
in favor of the Lessor, its Parent and Subsidiaries.

Taxes:

Sales or use taxes would be added to the Equipment Cost or collected on the
gross rentals, as appropriate.

Additional Covenants:

There shall be no actual or threatened conflict with, or violation of, any
regulatory statute, standard or rule relating to the Lessee, its present or
future operations, or the Equipment.

All information supplied by the Lessee shall be correct and shall not omit any
material statement necessary to make the information supplied not be
misleading.  There shall be no material breach of the representations and
warranties of the Lessee in the Lease. The representations shall include that
the Equipment Cost of each item of the Equipment does not exceed the fair and
usual price for like quantity purchased of such item and reflects all
discounts, rebates and allowances for the Equipment given to Lessee by the
manufacturer, supplier or any other person including, without limitation,
discounts for advertising, prompt payment, testing or other services.

Conditions Precedent to
Each Lease Term
Commencement:

1.   No material adverse change in the financial condition, operation or
     prospects of the Lessee prior to funding.

2.   Completion of the documentation and final terms of the proposed financing
     satisfactory to Lessor and Lessee and Lessor's and Lessee's counsel.

3.   Results of all due diligence, including lien, judgment and tax searches and
     other matters Lessor may request shall be satisfactory to Lessor and
     Lessor's counsel.

4.   Receipt by Lessor of duly executed Lease documentation in form and
     substance satisfactory to Lessor and Lessee and its counsels.

5.   Lessor shall receive title and a valid and perfected first priority lien
     and security interest in all Equipment acquired through the use of this
     Commitment and Lessor shall have received satisfactory evidence that there
     are no liens on any Equipment except as expressly permitted herein.

6.   Lessor shall be satisfied with the amount, type, and terms of all insurance
     maintained by the Lessee on Lessor's Equipment. Lessee shall deliver copies
     of all such insurance policies together with an endorsement naming Lessor
     as loss payee and additional insured.

7.   Copies of invoices and proof of payment on the sale and leaseback portion.

8.   Lessee on an on-going basis throughout the Lease shall provide to Lessor
     its quarterly financial statements and press releases, if any.





                                       66
<PAGE>   4
Fees and Expenses:

The Lessee shall be responsible for the Lessor's reasonable expenses (including
legal expenses) in connection with the transaction. Such expenses will not
exceed $5,000 without the expressed written consent of Lessee.

Law:

This letter and the proposed Lease are intended to be governed by and construed
in accordance with Illinois law without regard to its conflict of law
provisions.

Indemnity:

Lessee agrees to indemnify and to hold harmless Lessor, and its officers,
directors and employees against all claims, damages, liabilities and expenses
which may be incurred by or asserted against any such person in connection with
or arising out of this letter and the transactions contemplated hereby, other
than claims, damages, liability, and expense resulting from Lessor or such
person's gross negligence or willful misconduct.

Confidentiality:

This letter is delivered to you with the understanding that neither it nor its
substance shall be disclosed publicly or privately to any third person except
those who are in a confidential relationship to you (such as your legal counsel
and accountants), or where the same is required by law and then only on the
basis that it not be further disclosed, which conditions the Lessee and its
agents agree to be bound by upon acceptance of this letter.

Without limiting the generality of the foregoing, none of such persons shall
use or refer to Lessor or to any affiliate name in any disclosures made in
connection with any of the transactions without Lessor's prior written consent.

Conditions of Acceptance:

This Commitment Letter is intended to be a summary of the most important
elements of the agreement to enter into a leasing transaction with Lessee, and
it is subject to all requirements and conditions contained in Lease
documentation proposed by Lessor or its counsel and acceptable to Lessee and/or
its counsel in the course of closing the lease described herein. Not every
provision that imposes duties, obligations, burdens, or limitations on Lessee
is contained herein, but shall be contained in the final Lease documentation
satisfactory to Lessor and Lessee and its counsel.

EACH OF THE PARTIES HERETO IRREVOCABLY AND UNCONDITIONALLY WAIVES ALL RIGHT TO
TRIAL BY JURY IN ANY SUIT, ACTION, PROCEEDING OR COUNTERCLAIM ARISING OUT OF OR
RELATED TO THIS LETTER OR THE TRANSACTION DESCRIBED IN THIS LETTER.

Commitment Fee:

The $20,000 Application Fee previously paid shall be applied to the Commitment
Fee. The Commitment Fee will then first be applied to Lessor's reasonable
expenses not to exceed $5,000 without Lessee's written consent and the
remainder will be applied on a prorate basis towards the





                                       67
<PAGE>   5

second month's rent for each Lease Term Commencement as Equipment is accepted
under this Lease Commitment.  Commitment Fee will be refunded if the Lessee and
Lessor do not execute lease documentation acceptable to both parties.

Commitment Expiration:

This Commitment shall expire on January 29, 1997, unless prior thereto either
extended in writing by the Lessor or accepted as provided below by the Lessee.

Should you have any questions, please call me. If you wish to accept this
Commitment, please so indicate by signing and returning the enclosed duplicate
copy of this letter to me by January 29, 1997.

Yours truly,

TRANSAMERICA BUSINESS CREDIT
CORPORATION-TECHNOLOGY FINANCE
DIVISION

By /s/ Gerald A. Michaud
Gerald A. Michaud
Senior Vice President - Marketing

Accepted this 22 day of May, 1997

By /s/ John Monahan
John Monahan
Chief Executive Officer





















                                       68