SUBORDINATED NOTE PURCHASE AGREEMENT

Exhibit 10.197

SUBORDINATED NOTE PURCHASE AGREEMENT

PHILIP E. ROSENSWEIG

and

BIOVEST INTERNATIONAL, INC.

Dated: September 10, 2007

LIST OF EXHIBITS

SUBORDINATED NOTE PURCHASE AGREEMENT

THIS SUBORDINATED NOTE PURCHASE AGREEMENT (this “ Agreement ”) is made and entered into as of September 10, 2007, by and between BIOVEST INTERNATIONAL, INC., a Delaware corporation (the “ Company ”), and Philip E. Rosensweig (the “ Purchaser ”).

RECITALS

WHEREAS, the Company has authorized the sale to the Purchaser of a Subordinated Promissory Note in the aggregate principal amount of Three Hundred Thousand dollars ($300,000) in the form of Exhibit A hereto (as amended, modified and/or supplemented from time to time, the “ Note ”);

WHEREAS, the Company wishes to issue to the Purchaser upon maturity of the Note shares of the Company’s common stock valued at $300,000 priced at the lower of: (i) $1.10 per share; or (ii) a discount of 15% to the volume-weighted average price of the Company’s common stock for the sixty days prior to maturity of the Note; in connection with the Purchaser’s purchase of the Note (the “Stock Payment”);

WHEREAS, the Purchaser desires to purchase the Note on the terms and conditions set forth herein; and

WHEREAS, the Company desires to issue and sell the Note to the Purchaser on the terms and conditions set forth herein.

AGREEMENT

NOW, THEREFORE, in consideration of the foregoing recitals and the mutual promises, representations, warranties and covenants hereinafter set forth and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree as follows:

1. Agreement to Sell and Purchase . Pursuant to the terms and conditions set forth in this Agreement, on the Closing Date (as defined in Section 2), the Company shall sell to the Purchaser, and the Purchaser shall purchase from the Company, the Note. The Note will mature on the Maturity Date (as defined in the Note).

2. Closing, Delivery and Payment .

2.1 Closing . Subject to the terms and conditions herein, the closing of the transactions contemplated hereby (the “ Closing ”), shall take place on the date hereof, at such time or place as the Company and the Purchaser may mutually agree (such date is hereinafter referred to as the “ Closing Date ”).

2

2.2 Delivery . At the Closing on the Closing Date, the Company will deliver to the Purchaser the Note and the Purchaser will deliver to the Company the proceeds of the Note and a fully executed Subordination Agreement subordinating the Note to the Company’s obligations to Laurus Master Funds and Accentia Biopharmaceuticals, Inc.

2.3 Payment Upon Maturity . In addition to the repayment of the Note as set forth therein, upon the Maturity Date the Company shall issue to the Purchaser that number of shares of the Company’s common stock determined by dividing $300,000 by the lower of (i) $1.10 or ii) an amount equal to the greater of a discount of 15% to the volume-weighted average price of the Company’s common stock for the sixty days prior to the Maturity Date or $0.01 per share (the “Stock Payment”).

2.4 Registration Rights . The common stock issued in the Stock Payment shall have “piggy-back” registration rights, as follows: In the event that the Company plans to file a registration statement with the U. S. Securities and Exchange Commission covering shares of common stock of the Company (“Registration Statement”) at any time after the Maturity Date, the Company shall provide written notice to Purchaser and Purchaser shall have 30 days to require in writing that all shares of common stock issued for the Stock Payment be covered in the Registration Statement. Notwithstanding the foregoing, the Company shall have the right full discretion to determine not to include the shares underlying the Stock Payment in any registration statement if the Company reasonably determines that such registration may adversely effect the registration statement, the offering described in the registration statement or otherwise adversely affect the Company, in which case the Company shall include the shares in the next appropriate Registration Statement filed by the Company.

3. Representations and Warranties of the Company . The Company hereby represents and warrants to the Purchaser as follows:

3.1 Organization, Good Standing and Qualification . Each of the Company and each of its Subsidiaries is a corporation, partnership or limited liability company, as the case may be, duly organized, validly existing and in good standing under the laws of its jurisdiction of organization. Each of the Company and each of its Subsidiaries has the corporate, limited liability company or partnership, as the case may be, power and authority to own and operate its properties and assets and, insofar as it is or shall be a party thereto, to (a) execute and deliver (i) this Agreement, (ii) the Note; (b) issue and sell the Note; (c) issue the common stock required for the Stock Payment. The Company and each of its subsidiaries is duly qualified and is authorized to do business and is in good standing as a foreign corporation, partnership or limited liability company, as the case may be, in all jurisdictions in which the nature or location of its activities and of its properties (both owned and leased) makes such qualification necessary.

4. Representations and Warranties of the Purchaser . The Purchaser hereby represents and warrants to the Company as follows (such representations and warranties do not lessen or obviate the representations and warranties of the Company set forth in this Agreement):

4.1 No Shorting . The Purchaser or any of its affiliates and investment partners has not, will not and will not cause any person or entity, to directly engage in “short sales” of the Company’s Common Stock as long as the Note shall be outstanding.

3

4.2 Requisite Power and Authority . The Purchaser has all necessary power and authority under all applicable provisions of law to execute and deliver this Agreement and to carry out its provisions. Upon its execution and delivery, this Agreement will be valid and binding obligations of the Purchaser, enforceable in accordance with their terms, except:

(a) as limited by applicable bankruptcy, insolvency, reorganization, moratorium or other laws of general application affecting enforcement of creditors’ rights; and

(b) as limited by general principles of equity that restrict the availability of equitable and legal remedies.

4.3 Investment Representations . The Purchaser understands that the Note and common stock for the Stock Payment are being offered and sold pursuant to an exemption from registration contained in the Securities Act based in part upon the Purchaser’s representations contained in this Agreement, including, without limitation, that the Purchaser is an “accredited investor” within the meaning of Regulation D under the Securities Act. The Purchaser confirms that it has exclusively relied upon his right to conduct due diligent inquiry into the Company and that Pur