The long term protective efficacy of recombinant hepatitis B vaccine, administered alone or concomitantly with hepatitis B immunoglobulin, was assessed in 263 healthy neonates of hepatitis B e antigen-positive mothers. Infants received the first dose of vaccine at birth; additional doses were given at either Months 1, 2 and 12 or Months 1 and 6. During the follow-up period, which ranged from 2 to 4 years, protective titers (> or = 10 mIU/ml) of anti-hepatitis B surface antibodies were found in virtually all infants who had responded to the primary course of vaccination. "Natural boosts," without persistent infection, were observed in only a small number of children. All children who were shown to have become chronic carriers were infected within the first year of life. No statistical difference in long term protective efficacy could be shown between the two vaccination schedules used or between the use of vaccine alone or vaccine plus hepatitis B immunoglobulin for either schedule.