The immunogenicity of a recombinant hepatitis B vaccine was evaluated in 35 hemodialysis patients who received a standard dose (20 micrograms) of the vaccine at 0, 1, 2 and 6 months. After the full vaccination course (month 7), 60% (21/35) of the patients had seroconverted (anti-HBs titer greater than or equal to 10 mIU/ml). The duration of protection lasted up to 18 months after the start of vaccination in 85.7% (18/21) of the responders. At that time, an additional dose was given to all the patients: 1-2 months later, the overall immunization rate had increased to 65.7% (23/35); lastly, in month 24 (i.e., 6 months after the booster dose), 62.5% (15/24) of the patients available for evaluation were still maintaining protective levels of anti-HBs antibodies. Comparable results had previously been obtained in 21 well-matched patients on our dialysis program who were vaccinated with a plasma-derived vaccine according to the recommended schedule.