The authors detected Epstein-Barr virus (EBV) virus capsid (VCA) antibodies of IgM and IgG type together with EBNA and heterophil antibodies in the sera collected from 1882 unselected patients without infectious mononucleosis. Out of them IgM type antibodies were found in 123 cases and in an additional group of 30 patients heterophil antibodies were detected together with EBV specific virus markers. Altogether 153 patients were considered as cases of primary EBV infection, or reinfection. Comparing the distribution of age groups of the 1729 and the 153 patients, the author observed the increased incidence of elderly cases among patients with actual EBV infection, particularly above 60 years of age (P < 0.001). The 1729 patients were composed of 141 main diagnostic groups and the 153 patients with actual EBV infection consisted of 30 main diagnostic groups of which more than one third (53 cases) were of alcoholic liver diseases and patients of HBsAg carriers. The authors suppose, that in the cases of alcoholic liver diseases and of HBsAg carriers the suspected "immunocompromised" condition of those patients resulted the actual EBV infection, or reinfection. In other cases, like virus infection or meningitis serosa, it is suspected that the EBV can be responsible producing the symptoms.