Exhibit 4.6

October 27, 2005

Omicron Master Trust

650 Fifth Avenue

24^th Floor

New York, New York

USA 10019

Attention:Brian Daly

Dear Sirs:

Re: Generex Biotechnology Corporation - Amendment to Jun 17 05 Additional Investment Right

We make reference to the additional investment right issued by Generex Biotechnology Corporation (the “Company”) to Omicron Master Trust (“Omicron”) on June 17, 2005 pursuant to which the Company, inter alia, granted to Omicron the right to purchase a $500,000 principal amount debenture (the “AIR”).

The Initial Exercise Date (as that term is defined in the AIR) of the AIR is expressed therein as the 181^st day after the date thereof. The Company hereby confirms that, in consideration of the exercise of the AIR by Omicron and the delivery to the Company of a Notice of Exercise in respect thereof on or before the close of business on October 27, 2005, the Company has agreed to abridge the Initial Exercise Date and to honor the aforementioned Notice of Exercise.

Yours truly,

Generex Biotechnology Corporation

/s/ Mark A. Fletcher

Mark A. Fletcher

Executive Vice-President, General Counsel

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