Subclinical and clinical cases of hepatitis B virus (HBV) infection in hospital personnel were recorded over a five-year period. Although our data indicate the existence of "high-risk areas" like laboratories, dialysis units or surgical wards, it was found that 50% of all HBV infections were observed outside these areas. During the same period, most of our inpatients were monitored for HBs-antigenemia. It could be demonstrated that more than 50% of all cases of HBs-antigenemia were not known before and were treated primarily for other reasons than for hepatitis B. As a consequence from our data and from the screening for environmental HBs-antigen on laboratory surfaces it may be concluded for the hospital routine: Even minimal contaminations with blood should be avoided, all personnel should be vaccinated against HBs-antigen, HBs-antigen should be determined in every inpatient to detect inapparent virus carriers.