We analyzed the bilirubin uridine diphosphate-glucuronosyltransferase (B-UGT) gene in 42 Japanese newborns with hyperbilirubinemia and determined that 21 infants were heterozygous while 3 was homozygous for Gly71Arg. Allele frequency of Gly71Arg was 0.32 in newborns with hyperbilirubinemia, which was significantly higher than 0.13 in healthy Japanese controls. This mutant allele is also prevalent among Korean and Chinese healthy controls with a frequency of 0.23 in both populations. However, this mutation was not detected in 50 healthy German controls. These data suggest that the high frequency of the Gly71Arg mutation of the B-UGT gene is associated with high incidence of neonatal hyperbilirubinemia in Japanese, Korean and Chinese populations.