The need for an additional dose of hepatitis B immune globulin (HBIg) was studied by comparing infants receiving 1 ml HBIg at birth followed by hepatitis B immunization, concomitant with DTP-polio vaccine, at 3, 4, 5 and 11 months (schedule E), with infants receiving the same schedule with additional HBIg at 3 months (schedule F). The immune response to recombinant hepatitis B vaccine (20 micrograms) was evaluated in 195 infants born to HBsAg-positive mothers allocated to groups E and F and compared with historic controls who received plasma vaccine (10 micrograms) according to schedule F. Blood samples were drawn at 0, 3, 4, 6, 11, 12 and 24 months of age. No difference in efficacy between the two schedules was observed; 8 and 6% of infants born to HBeAg-positive HBsAg carrier mothers in groups E and F, respectively, became HBsAg carriers. Passively acquired antibodies at birth remained present for about 5 months in most infants. The seroprotection rates (anti-HBs > or = 10 IU l-1) were over 90% at all time points and similar for groups E and F. The titres of anti-HBs attained during the first 6 months were statistically lower (p < or = 0.02) for group E than for group F but similar thereafter. Anti-HBs titres in infants receiving the recombinant vaccine were significantly lower than in infants receiving the plasma vaccine (p << 0.001). Supplemental doses of HBIg in infants receiving a high dose of HBIg ( > 200 IU) at birth and the first dose of vaccine at the age of 3 months are not advised.