In order to determine whether reinforced vaccinations improve the immune response among uremic patients, three vaccination schedules with hepatitis B surface antigen vaccine (Institut Pasteur Production) were compared. A total of 215 hemodialysis patients treated in HBV free units were randomly allocated to Group I (3 injections of 1 ml), Group II (3 injections of 2 ml) and Group III (4 injections of 1 ml). Immune response was evaluated in 204 patients. The percentages of responders within 12 months after the first injection (greater than = 10 mIU/ml on 2 successive blood specimens) were: 45.6%, 75.0% and 69.4% in Group I, Group II and Group III respectively. The geometric mean peak values of anti-HBs observed 6 months after the first injection among the responders were: 60, 192 and 268 mIU/ml respectively. One month after a booster dose given to 182 patients 14 months after the first injection, anti-HBs levels were 144, 1123, 524 mIU/ml respectively, and the frequency of patients with an anti-HBs titer greater than = 50 mIU/ml was 68%, 82% and 75% respectively. These results led us to discard the use of Protocol I for these immuno-depressed patients while it is quite satisfactory in healthy subjects; they also show that Protocol II and III give better results than Protocol I, but that they cannot be statistically differentiated. We conclude that response rates and anti HBs antibody titers can be significantly improved in chronic hemodialysis patients with reinforced vaccination protocols.