A complex study of 1273 healthy children of creches and kindergartens where no viral hepatitis occurred for a long time revealed 39 children (3.1%) with an increased activity of glutamine-pyroracemic transaminase in the blood serum. Viral hepatitis was diagnosed in 12 (0.94%) of them as a result of clinical examination (an icteric form in 1, and a nonicteric form in 11 cases). The presence of asymptomatic form of infection could be supposed in 17 other children (1.3%). The incidence of increased activity of the enzyme in the serum of "healthy" children was definitly connected with the viral hepatitis incidence registered in the town during the year as a whole, and by seasons. This permitted to prognosticate the spread of viral hepatitis in the given populated locality. By complex laboratory examination of children in collective bodies it was possible to detect the latene foci and the latently coursing epidemic process of viral hepatitis.