DNA probes were prepared from the 5'-terminal portion of four cDNA clones encoding human phenol and bilirubin UDP-glucuronosyltransferases (UGTs). An additional sequence common to all four clones was isolated from the 3'-terminal portion of one of the clones (UGT1A1). The four specific and the one common DNA sequences were used as probes on a panel of 16 human--rodent somatic cell hybrid DNAs by Southern-blot analysis. The results obtained indicate that all four cDNA clones are encoded by gene(s) located on human chromosome 2.