The intensity of detection and time course of the main markers of virus infection were studied in subjects who had contacts with patients in 74 foci with chronic active hepatitis, 52 with chronic persisting hepatitis and 41 with chronic hepatitis of unknown etiology. A high (up to 80.7%) frequency of detection of HBsAg, anti-HBs, anti-HBc was established in contact subjects which showed a trend of growth with the increase of the time of their contact with the source of infection.