Three injections of alum hepatitis B vaccine (HB vaccine) were given to 26 Senegalese infants, the first when they were less than 1 month old, and the second and third after 1-month intervals. 94.7% of the neonates whose serum was negative for hepatitis B surface antigen and antibodies against the surface antigen (anti-HBs) showed a specific anti-HBs response. Anti-HBs titres in the neonates were similar to those previously obtained in Senegalese children aged aged 1-24 months. HB vaccine was without sid-effects and was immunogenic in the neonates, irrespective of the hepatitis-B-marker status of the mothers or the children.