ExactAntigen can help molecular biologists, immunologists, and other researchers track down everything from samples of the cholera toxin to monoclonal antibodies against the appetite-adjusting hormone leptin. Created by Hanqing Xie of Synatom Research in Ringoes, New Jersey, the free site trolls thousands of Web sites--mainly from commercial suppliers--and other sources to locate providers of antibodies and reagents.

Users can search by categories such as gene, organism, and disease. The results often list other molecular products, such as gene-blocking siRNA molecules, along with publications and relevant patents.