Human tissues contain at least three well-characterized cytoplasmic sulfotransferase (ST) enzymes, dehydroepiandrosterone (DHEA) ST and two of phenol ST (PST). DHEA ST catalyzes the sulfation of DHEA and other steroids. We cloned and expressed two cDNAs for human liver DHEA ST. The cloning strategy involved the design of PCR primers directed against two conserved domains in ST proteins. These primers were used to generate a specific PCR product that was then used successfully to clone cDNAs for DHEA ST from a human liver cDNA library. Two cDNAs were isolated that were approximately 1.1 and 1.8 kb in length. These two clones had identical open reading frames. Both cDNAs produced enzymatically active DHEA ST protein in a mammalian expression system. Northern blot analysis confirmed the presence of 1.1 and 1.8 kb transcripts in human liver. cDNAs for a number of eukaryotic enzymes have now been cloned, and they share significant sequence homology. These ST cDNAs appear to fall into distinct groups on the basis of amino acid sequences of the proteins that they encode, thus demonstrating that the enzymes comprise a gene superfamily. We have also isolated, a genomic clone for human DHEA ST that contains approximately 3 kb of 5'-flanking sequence, exon 1 and 1.7 kb of intron 1. Characterization of the structure and regulatory elements of this gene should help to elucidate mechanisms involved in the regulation of DHEA ST in humans.