Formalin-inactivated hepatitis B vaccine was given at 0, 1 and 6 months to 22 medical staff members and to 37 haemodialysis patients. After vaccination with 20 micrograms surface antigen (HBsAg), seroconversion occurred in 95% of the staff members. Following immunisation with a double dose, only 74% of the haemodialysis patients developed antibodies against HBsAg (anti-HBs). Anti-HBs levels were lower in the patient group and 6 responders (23%) became anti-HBs-negative within 2 years. 40 other haemodialysis patients were immunised at monthly intervals with either three doses of 3 micrograms or three doses of 27 micrograms heat-inactivated hepatitis B vaccine. Seroconversion was achieved in 60% of the patients in the 3-micrograms group and in 95% of the patients in the 27-micrograms group. Anti-HBs levels increased significantly when the high dose was used. Although the study design does not allow a definite conclusion, it appears that the immunogenicity per microgram HBsAg is higher for the heat-inactivated vaccine than for the formalin-inactivated vaccine. The findings further indicate that decreased immune response to hepatitis B vaccination in haemodialysis patients can be improved by increasing the dose of the vaccine. A booster injection should be considered in these patients within 2 years after the first vaccination.