Sera from 90 patients with sarcoidosis were examined For antibodies to Epstein-Barr virus (EBY)-associated antigens [viral capsid antigens (VCA) and early antigens (EA)] and for antibodies against a variety of other viral antigens including herpes simplex, varicella, and cytomegalovirus (CMV) antigens. Antibody titers against VCA were, on the average, 3 times higher in sarcoidosis patients than in age-matched control groups. In sarcoidosis patients, 98% were positive against 85.5% in the controls. The differences were statistically significant both with respect to titer levels and rates of positivity. Twenty-one sera which had high titers (≥160) of antibodies to VCA were also examined for antibodies to early antigens; low titers were found in 7 sera. Heterophil antibodies, also in low titers, were found in 8 of 90 sarcoidosis patients. The rates of antibodies to herpes simplex and CMV were also significantly higher among the sarcoidosis patients than in the control groups, whereas tests for other antibodies were on the same level as in the control materials. The EBV-associated VCA was demonstrated in 5 of 13 cultures derived from explanted sarcoid lymph nodes. The findings do not provide evidence of an etiologic role of EBV in sarcoidosis. The moderately elevated titers of antibodies against EBV, CMV, and herpes simplex antigens may be due to nonspecific factors like increased reactivity to certain antigens or an increased susceptibility to the respective infections or a higher tendency for recurrences of latent infections.