Comparative studies of sera from 710 patients with viral hepatitis and contacts were made during the 1958-1973 period for hepatitis antigens (Au antigen and the Botevgrad antigen). The percentage of virus hepatitis in patients positive for the Au and the Botevgrad antigens varied in different years. The percentage of those positive for the Au antigen ranged from 50 in 1958 to 8.8 in 1970-1971, while for the Botevgrad antigen--it ranged from 32.6 in 1962-1963 to 6.1 in 1966. In case of contacts, mostly in the 7-14 age group the sera positive for the Au antigen were found in a low percentage (2.09 percent) of cases; as to the Botevgrad antigen, 20 persons were found positive during various epidemics (55 percent). Simultaneous presence of both antigens was found in 4 of the 710 patients with virus hepatitis (0.56 percent), and in 2 of 431 contacts (0.46 percent).