An extensive menu of immunoassays. We believe we have the most extensive menu of validated multiplexed biomarker immunoassays in the industry, enabling us to cast a wide net in the search for clinically relevant biomarker patterns

JOINDER AGREEMENT TO

INVESTORS’ RIGHTS AGREEMENT

May 6, 2008

     By executing this Joinder Agreement to Investors’ Rights Agreement (this “Agreement”), the undersigned, Mark J. Gainor (“Purchaser”), hereby agrees to become a party to that certain Investors’ Rights Agreement (the “Investors’ Rights Agreement”), dated as of October 12, 2007, by and among Rules-Based Medicine, Inc., a Delaware Corporation (the “Company”) and the Stockholders (capitalized terms used but not defined in this Agreement shall have the meanings ascribed to them in the Investors’ Rights Agreement). Purchaser hereby acknowledges and agrees to the following:

     a. Purchaser is acquiring shares of Common Stock of the Company pursuant to that certain Common Stock Purchase Agreement, dated as of May 6, 2008, by and between the Company and Purchaser (the “Common Stock Purchase Agreement”).

     b. Purchaser is acquiring shares of Series A-1 Preferred Stock of the Company pursuant to that certain Stock Purchase and Sale Agreement, dated May 6, 2008, by and between EGI-Fund (08-10) Investors, L.L.C. and Purchaser (the “Preferred Stock Purchase Agreement”).

     c. Purchaser shall be treated as a Common Holder and listed on Schedule B of the Investors’ Rights Agreement with respect to the shares of Common Stock that he is purchasing pursuant to the Common Stock Purchase Agreement.

     d. Purchaser shall be treated as an Investor (but not a Lead Investor) and listed on Schedule A of the Investors’ Rights Agreement with respect to the shares of Series A-1 Preferred Stock that he is purchasing pursuant to the Preferred Stock Purchase Agreement.

     e. Purchaser shall have all of the rights, and shall observe all the obligations, applicable to the Common Holders, the Investors, and the Major Holders pursuant to the Investors’ Rights Agreement.

[Signature Page Follows]

IN WITNESS WHEREOF, the undersigned has executed this Agreement as of the date first written above.

		MARK J. GAINOR
				/s/ Mark J. Gainor
		Name:		Mark J. Gainor
		Number of Shares:		Common: 337,838, Series A-1 Preferred: 143,943
		Address:		5800 N. Bay Road
				Miami Beach, FL 33140
		Phone:		305 ###-###-####
		Fax:		305 ###-###-####
		Email:		***@***

Signature Page to
Joinder Agreement to Investors’ Rights Agreement