Normal values of all IgG subclasses were determined using a sensitive ELISA in children aged from newborn to 14 years. The upper and lower limits of normal values of all IgG subclasses were obtained in all the age groups using 29 umbilical cord blood samples from full‐term newborns and 308 venous blood samples from normal infants and children. The trends in the levels of IgG1, IgG2 and IgG3 with age were almost similar to previous reports. IgG4 levels decreased gradually until reaching the lowest level at 7 to 12 months and increased gradually with age, reaching a plateau at 12 to 14 years of age. Thus, the lower limit of serum IgG4 levels was determined using our method.

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One hundred infants born to hepatitis‐Be antigen (HBeAg)‐negative carrier mothers were followed with or without the administration of hepatitis‐B vaccine (HB vaccine) and/or hepatitis‐B hyperimmune globulin (HBIG). Among the infants without treatment, 7.6% of the infants born to the antibody‐to HBeAg (anti‐HBe)‐positive carrier mothers and 14% of those born to the carrier mothers without HBeAg and anti‐HBe developed HBs‐antigenemia, whereas none of the infants treated became positive for HBsAg. The results indicate the necessity for preventive measures for the babies born to HBsAg‐carrier mothers, regardless of their HBeAg state.