One hundred and fourteen children, born to HBsAg-positive mothers received in the first year of life passive active prophylaxis for hepatitis B virus (HBV). They have been followed up to 10 years. A booster dose given in a cohort at the 5th year does not seem to increase protection against HBV. No difference in immunological memory was present at the 10th year between the group of children who had received the booster dose at 5 years of age and the group who did not.