Two hundred and seventy-seven infants born to hepatitis B surface antigen (HBsAg)-negative noncarrier mothers had been divided into 3 groups to receive 1 microgram, 2 micrograms or 5 micrograms of plasma derived hepatitis B vaccine and were followed up annually to the age of 6. At the end of the follow-up period, the antibody to HBsAg (anti-HBs) positive rates in these 3 groups were 63.0% (58/92), 77.9% (74/95) and 83.3% (75/90), respectively (group 1 vs. group 2, p less than 0.05; group 1 vs. group 3, p less than 0.01; group 2 vs. group 3, p greater than 0.05). Among the initial responders, 25 of 38 (65.8%) with low initial anti-HBs titers (10-100mIU/ml) and 18 of 79 (22.8%) with medium initial anti-HBs titers (101-1,000mIU/ml) were found to be anti-HBs seronegative, while only 2 of 136 (1.5%) with high initial anti-HBs titers (greater than 1,000 mIU/ml) lost their anti-HBs (P less than 0.01). None of the vaccinees became HBsAg positive but 1 initial responder became positive for anti-HBc at the age of 4. Twenty-five initial nonresponders and 18 initial responders who lost their anti-HBs at the age of 2 received a second booster of vaccination at the age of 3. Five (20.0%) of the initial nonresponders and 17 (94.4%) of the initial responders responded to the second booster. The annual incidence of natural booster was 2.1%. In conclusion, the standard doses of 5 micrograms plasma-derived vaccine tend to be the best choice for immunization of infants born to noncarrier mothers in Taiwan.(ABSTRACT TRUNCATED AT 250 WORDS)