In the present study the reactivity of IgG and IgM antibodies against HSV-1 structural and nonstructural proteins was analyzed by Western blot analysis (WBA) and radioimmunoprecipitation followed by polyacrylamide gel electrophoresis (RIPA-PAGE). It was demonstrated that IgM and IgG antibodies were directed against viral immediate-early, early, and late proteins. Following acute primary HSV infection, the early IgM antibody response in general was found to be directed against nonglycosylated structural proteins, viral early and immediate-early polypeptides. IgM antibodies against viral glycoproteins were found inconsistently. IgG antibodies against viral glycoproteins and other structural proteins with an apparent molecular weight of 56 kD, 45 kD, and 39 kD could be detected early in infection. Viral early and immediate-early proteins were poorly recognized by IgG antibodies in acute primary infections. In recurrent HSV infections, IgM antibodies revealed a less complex reaction with viral polypeptides. Thus, such IgM antibodies reacted predominantly with viral nonglycosylated structural proteins. In contrast, IgG antibodies from patients with recurrent infections strongly recognized viral structural, early, and immediate-early proteins. In seropositive individuals without obvious symptoms of acute infection, the most prominent antibody response was directed against gB and gD.