A herpes simplex virus subunit vaccine has been tested for immunogenicity and protective efficacy in animal models. The vaccine is a mixture of the viral glycoproteins gB and gD expressed in mammalian cells as secreted carboxyl terminal truncated derivatives. The antigens have been combined with several adjuvants, including a lipophilic derivative of a muramyl tripeptide, MTP-PE, and administered in a stable, low-oil emulsion. Titers of antibody that are threefold to 15-fold greater than those obtained with alum and within twofold of those generated with complete Freund's adjuvant are elicited in animals, including primates. Prophylactic immunization of guinea pigs provides nearly complete protection against intravaginal challenge with herpes simplex virus type 2. Treatment of previously infected guinea pigs reduces the frequency and severity of recurrent disease, although variations in efficacy dependent on the antigen, adjuvant, and dosing regimen employed are observed. The immunogenicity of this vaccine in animals provides the rationale for further testing in human clinical trials.