Among persons with herpes simplex virus type 2 infection, approximately 75% are asymptomatic and can be identified only by serologic testing with type-specific assays. Among serologic assays, the Western immunoblot assay, the glycoprotein G-2 immunodot assay, and the glycoprotein G-2 enzyme immunoassay appear sensitive and type-specific, although the latter appears less sensitive in immunocompromised individuals. Commercial enzyme immunoassays give inaccurate or misleading results regarding virus type. In epidemiologic studies, type-specific serologic assays have been used prospectively to study risk factors for the transmission of genital herpes in heterosexual couples, to identify couples at unsuspected risk for transmission of genital herpes during pregnancy, and to assess the role of genital herpes as a risk factor for human immunodeficiency virus infection in heterosexuals.