A longitudinal study of serum IgG and IgA antibody titers to Epstein-Barr virus (EBV) viral capsid antigen (VCA) was carried out in 218 homosexual men at various stages of human immunodeficiency virus (HIV) infection. The serum samples tested were obtained from the following groups: 24 HIV seroconverters, 41 persistently HIV-seropositive asymptomatic individuals, 22 seropositives who developed AIDS-related complex (ARC), 29 HIV seropositives who developed lymphadenopathy syndrome (LAS), 35 HIV seronegatives with LAS, 36 asymptomatic HIV seronegatives, and 31 AIDS patients. Blind-tested samples were titrated for IgG and IgA EBV-VCA antibodies by immunoperoxidase assay (IPA). Cross-sectional analysis indicated that all HIV-seropositive subjects exhibited significantly elevated EBV IgG and IgA antibody titers compared with HIV-seronegative subjects. The proportions with EBV-VCA IgA antibodies at a titer of greater than or equal to 128 rose during the course of HIV infection and progression of the disease: 8% in HIV seronegatives, 11% in HIV seronegatives with LAS, 25% in HIV seronegatives prior to HIV seroconversion, 44% in asymptomatic HIV seropositives, 34% in LAS, 50% in ARC, and 58% in AIDS patients. An increase in EBV-VCA IgG and IgA titers was detected following HIV seroconversion and in samples obtained 6 months before disease progression to LAS. These data suggest the possible involvement of EBV in the natural history of HIV infection and disease progression. The possibility that EBV-VCA IgA antibody levels would be of value in prediction of progression of HIV-related illness is discussed.