Two hundred infants and two hundred preschool children were randomly assigned to receive either 10 mu g of recombinant hepatitis B vaccine (GenHevac B) intramuscular ly (IM) or 2 mu g intradermally (ID) in the deltoid region at 0, 1 and 6 months. Antibody to hepatitis B surface antigen (anti-HBs) was tested eight weeks after the third vaccine dose. Standard dose IM and low-dose ID administration of recombinant hepatitis B vaccine produced comparable rates df anti-HBs equal to or higher than 20 mIU ml(-1) infants (98% and 94%, respectively) and preschool children (98% and 100%, respectively). Although IM vaccination produced higher anti-HBs concentrations than ID vaccination both in infants (geometric mean titre-GMT, 935 versus 621 mIU ml(-1)) and preschool children (GMT 1393 versus 804 mIU ml(-1)), the differences were not statistically significant (p > 0.05). The preschool children tended to have higher anti-HBs concentrations than the infants. No clinically serious adverse effects were observed in both vaccine groups; however induration and hyperpigmentation at the injection site were more often seen in the study population that was vaccinated intradermally. We conclude that intradermal administration of 2 mu g recombinant hepatitis B vaccine is safe and effective in infants and preschool children, and may be an acceptable, less expensive alternative to full-dose IM vaccination for mass immunization, especially in developing countries. (C) 1998 Elsevier Science Ltd. All rights reserved.