In the years 1986-90 530 consecutive patients with acute hepatitis were hospitalized in the Department of Hepatology of the Institute of Infectious and Parasitic Diseases in Warsaw. Hepatitis A was diagnosed in 34 cases (6.4%), hepatitis B in 436 (82.3%), CMV infection in 5 (0.9%) and 55 cases (10.4%) were classified as hepatitis non-A, non-B. In 47 cases (85%) of non-A, non-B hepatitis in 8 (15%) the source of infection was unclear. In 50% of patients with parenteral exposure transaminases remained elevated for longer than 6 months, while all patients with no known exposure recovered.