We report here three high-density maps of variations found among 48 Japanese individuals in three uridine diphosphate glycosyltransferase (UGT) genes, UGT2A1, UGT2B15, and UGT8. A total of 86 single-nucleotide polymorphisms (SNPs) were identified through systematic screening of genomic regions containing these genes: 8 in 5' flanking regions, 7 in coding regions, 67 in introns, 3 in 3' untranslated regions, and 1 in a 3' flanking region. We also discovered 14 variations of other types. Of the 86 SNPs, 63 (73%) were considered to be novel on the basis of comparison of our data with the Database of SNPs (dbSNP) of the National Center for Biotechnology Information. Among the seven SNPs identified in exonic sequences, five were non-synonymous changes that would result in amino-acid substitutions. The collection of SNPs derived from this study will serve as an additional resource for studies of complex genetic diseases and responsiveness to drug therapy.