An epidemiological survey of hepatitis B virus infection has been carried out in medical and paramedical employees of the Hospital of Parma, in order to identify high-risk groups and to estimate how many of subjects might be immunized with newly available but expansive vaccine. Radioimmunoassay procedures were used to detect the hepatitis B surface antigen (HBsAg) and the corresponding antibody (anti-HBs) in serum samples from 1682 hospital workers. Among these person tested, HBsAg was present in 57 (3.4%) and anti-HBs in 438 (26.3%); at least one of the two markers was found in 495 (29.4%). The prevalence of HBsAg and anti-HBs was related more closely to age, years and kind of occupation, than to clinical service (i.e. renal dialysis or medical services) and title (physician, nurse, laboratory technician, support staff.