Infants born to HBsAg-positive women were randomly assigned to receive either the plasma-derived hepatitis B vaccine or the yeast-derived recombinant hepatitis B vaccine within 12 h of birth, simultaneously with HBIg. The second and third doses of both vaccines were given at 1 and 6 months of age respectively. Two hundred and twenty-two infants received two doses, and 80 infants received three doses of either vaccine. Five infants were found to be HBsAg-positive at 6 months of age. Four of these infants had received the plasma vaccine and the remaining infant the recombinant vaccine. Anti-HBs was present in all the HBsAg-negative infants at 6 months of age. The titres of anti-HBs were similar in both groups of infants who had received either the plasma or the recombinant hepatitis B vaccine. No major adverse reactions were reported with either vaccine. The preliminary results from this study suggest that the yeast-derived recombinant hepatitis B vaccine is safe, immunogenic and at least as effective as the plasma-derived hepatitis B vaccine in preventing the HBsAg carrier state in infants born to HBsAg-positive women.