The UDP glucuronosyltransferase gene UGT2B2 is constitutively expressed in rat liver, and the enzyme has been shown to conjugate glucuronic acid with various endogenous steroids, especially etiocholanolone and androsterone. We have cloned and sequenced much of the UGT2B2 gene and 5'-flanking (247 bp) and 3'-flanking (734 bp) regions. The gene contains six exons spanning about 15.3 kb. Translation begins at nucleotide 36 of exon 1 and terminates with 280 coding nucleotides into exon 6, encoding a protein of 530 amino acids (calculated Mr of the unmodified chain = 60,913). We have determined that the UGT2B2 full-length cDNA is 1,974 bp. Northern hybridization revealed that the hepatic UGT2B2 transcript is detectable 4 days before birth, becomes markedly elevated in the neonate, and is even further increased at 3 and 12 weeks of age in the liver of both male and female rats.