Medical, nursing, laboratory and other staff of the Mersey Regional Blood Transfusion Centre at risk of acquiring hepatitis B were vaccinated against the virus with a recombinant vaccine. Altogether, 86% staff developed greater than 10 mIU/ml antibody to hepatitis B virus surface antigen after immunisation but the proportion was lower in older staff. After a further injection of vaccine was given to poor and non-responders the overall proportion responding rose to 93%. The difference in response between the sexes was significant. Women had a higher rate of response and, among those persons responding, women developed a higher concentration of antibody.