Epidemiological investigations of 1883 cases of acute viral hepatitis type B reported in two voivodships (Piotrków, Sieradz) has been analysed. In 1104 cases (58%) parenteral procedures for therapeutical and diagnostic purposes have been performed during 6 months before the onset of disease. The incidence of cases after medical procedures was the highest in children aged 0-4 years (67%) and adult persons aged over 50 years (68%). Home contacts with HBV carriers and/or recoverers gave only 342 cases (18.2%). Professional infections occurred in 117 medical workers (6.2%). At that time both voivodship had high hepatitis B morbidity ranging 91.7/100,000 in Piotrków voivodship in 1986 over two times higher than in the whole country (38.9/100,000).