We screened DNAs from 48 Japanese individuals for single-nucleotide polymorphisms (SNPs) in genes encoding 13 cytochrome P450 (CYP) enzymes and 14 aldehyde dehydrogenases (ALDHs) by directly sequencing their entire genomic regions except for repetitive elements. This approach identified 810 SNPs and 96 insertion/deletion polymorphisms among the 27 genes. Of the 810 SNPs, 229 were identified among the CYP genes and 581 in the ALDH genes; of the total, 48 SNPs were located in 5' flanking regions, 619 in introns, 91 in exons, and 52 in 3' flanking regions. These variants should contribute to studies designed to investigate possible correlations between genotypes and phenotypes of disease susceptibility or responsiveness to drug therapy.