Fifty-three children who failed to respond to four doses of plasma hepatitis B (HB) vaccine (anti-HBs titre < 10 IU l-1) were divided into two groups and received revaccination with either three doses of recombinant HB vaccine (10 micrograms/dose, by 0, 1, 6 month schedule; group A) or two additional doses of plasma HB vaccine (5 micrograms/dose, by 0, 1 month schedule; group B) respectively. Thirty-two vaccinees in group A had a response rate (with anti-HBs > 10 IU l-1) of 53.1% (17/32), 87.5% (28/32), and 100% (32/32) after first, second and third doses of the vaccine respectively. Twenty-one vaccinees in group B had a response rate of 61.9% (13/21) after two additional doses of plasma vaccine. High anti-HBs titres (> 1000 IU l-1) were noted in 50% of the vaccinees in group A after three doses of vaccine. Comparing anti-HBs response between group A and group B after two additional doses of HB vaccine, group A had a higher anti-HBs titre (geometric mean titre 104.7 IU l-1 versus 75.9 IU l-1) along with a better seroconversion rate (87.5 versus 61.9%). However, the differences in vaccine dose between the two groups may also be a contributory factor. Our findings indicate that three doses of recombinant HB vaccine were invariably effective in eliciting a good immune response in previous non-responders to the four doses of plasma HB vaccine. Therefore, it is speculated that these young vaccinees who did not respond to four doses of plasma HB vaccine may not be real non-responders, but hyporesponders.