Summary The feasibility of introducing low dose (5 μg) hepatitis B (HB) virus vaccination at birth and again 1 and 2 months later as part of an existing primary immunisation programme of childhood, was assessed in 662 healthy newborn Singapore children. The vaccine (B-Hepavac, Menck, Sharp and Dohme) was given to three neonatal groups: those born to (i) HB surface antigen (sAg)-negative mothers, (2) HBsAgpositive/HBeAg-positive mothers and (3) HBsAg-positive/HBeAg-negative mothers. A dose of 5 μg was compared in a randomised study with the more usual 10 μg dose given at the same intervals. Neonates born to HBsAg-positive/HBeAg-positive mothers were also given hepatitis B immunoglobulin (HBIg) at birth. The 5 μg dose of vaccine was as immunogenic as the 10 μg dose in all three groups of children studied. At 1 year, anti-HBsAg seroconversion among infants of antigen-negative mothers was 95·8% for the 5 μg dose and 91·9% for the 10 μg dose. Suppression of anti-HBsAg formation was not seen even when maternal anti-HBsAg was present or HBIg given. Among infants born to HBsAg-positive/HBeAg-positive mothers, passive plus active immunisation was 100 % protective at doses of 5 μg and 10 μg vaccine in the newborns who were HBsAg-negative at 24 h. Seroconversion after both the 5 and 10 μg doses of vaccine was reduced, however, to 88% in each group of infants who were already HBsAg-positive at 24 h of age. Overall, passive plus active immunisation as well as HB vaccine alone (5 μg dose), given within the existing but expanded primary immunisation programme of childhood, was effective in preventing infection and the chronic carrier state in newborns exposed to risk of HB virus infection during infancy.