The efficacy and safety of a hepatitis B vaccine (Pasteur Institute) has been evaluated in 93 healthy members of the medical staff and in 28 patients undergoing chronic haemodialysis. Following 3 injections of vaccine (each 5 micrograms) at monthly intervals, 94% of the healthy subjects and 61% of the patients were already successfully immunized 4 months after commencement of the vaccination course. Those who did not respond initially received an additional dose at 6 months, which induced seroconversion in several more cases, resulting in the successful immunization of 98% of healthy subjects and 75% of haemodialysis patients. Immune response was sex- and age-dependent. Peak anti-HBs concentrations in responders at 6 months were 643, 325, and 194 mU/ml in healthy women, healthy men, and in patients, respectively. None of the staff members developed clinical or biochemical signs of hepatitis or of any other disease. Markers of hepatitis B virus infection were detected in 3 healthy subjects and in 6 dialysis patients.