During the period 1980-1989 in Okinawa, Japan, serologic markers of hepatitis B infection (hepatitis B surface antigen; HBsAg, antibody to hepatitis B core antigen; anti-HBc) were investigated in nursery school children (1-4 years of age). Prevalences of HBsAg were 1.1-1.5% in the period from 1980-1984, but decreased to under 1.0% in the period from 1985. In 1989 there were two carriers in nursery schools, both born in 1985 or fathers who were HBsAg carriers. Prevalences of anti-HBc were 3.3-7.1% in the period from 1980-1983 with a decrease to 0.5% by 1988. Since hepatitis B vaccine was available for neonates whose mothers were HBsAg carriers with hepatitis Be antigen (HBeAg) and for nursery school children in 1983, hepatitis B virus infection among nursery school children and HBsAg carriers due to transmission from mother-to-child were markedly reduced. This strategy for immunization is useful in endemic areas. Immunization for children whose fathers are HBsAg carriers may also be necessary.