Objective. To determine whether hepatitis B vaccination given intracutaneously (IC) is more effective than intramuscularly (IM) in primary non-responding haemodialysis patients. Design. A prospective, randomized study of antibody responses to hepatitis B vaccine given IC or IM, in 25 haemodialysis patients. Outcome measures were rates of seroconversion, mean and geometric mean levels of antibody achieved, and antibody levels 1 year after vaccination. Results. With a dosing schedule of 10 mu g vaccine once a week IC in the skin overlying the deltoideus muscle of the non-dominant arm during 12 consecutive weeks, antibody levels to hepatitis B surface antigen (anti-HBsAg) of 10 IU/l or more were achieved in nine of 10 evaluable patients, with a geometric mean of 70 IU/l. Nine months after the end of the vaccination anti-HBsAg levels had dropped to 9 +/- 4 IU/l (M +/- SE), with a geometric mean of 5 IU/l, in the nine remaining evaluable patients. With a dosing schedule of 40 mu g vaccine i.m. in the deltoideus muscle of the non-dominant arm at 0, 1, and 3 months, anti-HBsAg levels of at least 10 IU/l were achieved in eight of 14 evaluable patients, with a geometric mean of 94 IU/l. Nine months after the end of the vaccination anti-HBsAg levels had dropped to 16 +/- 7 IU/l, with a geometric mean of 9 IU/l, in the nine remaining evaluable patients. Anti-HBsAg levels at 8 and 12 weeks were higher in the IC than in the group receiving vaccine IM (at 8 weeks 134 +/- 76 vs 39 +/- 20 IU/l, P < 0.05, and at 12 weeks 188 +/- 98 vs 47 +/- 18 IU/l P < 0.01). The half-time of anti-HBsAg is about 13 weeks, both when the averaged absolute and when the geometric mean levels are used for the estimate. Conclusion. The intracutaneous route is a less practical but effective method of vaccination against hepatitis B in primary non-responding haemodialysis patients. The weekly 10 mu g vaccine IC scheme resulted in the fastest development of protective antibody levels, within 8 weeks, which may be useful in previously non-immune persons who may be infected with hepatitis B virus (e.g. needle-stick accidents).