One experimental AIDS vaccine is the gp120 vaccine. The HIV envelope glycoprotein 120 is manufactured through recombinant DNA technology and used as an immunogen. Antibodies directed against gp120 can neutralize HIV-1, and gp120 can also stimulate certain types of cell-mediated immune responses. Because many immunogens, including candidate HIV vaccines, may evoke relatively weak immune responses, the use of adjuvants, or substances that augment immune responses to vaccines, is of interest. MTP-PE/MF59, composed of the immunomodulator MTP-PE combined with MF59 emulsion, appears to be a promising adjuvant and has been selected for studies with the gp120 vaccine.