We have isolated cDNA clones encoding phenol- and monoamine-sulfating phenolsulfotransferases, using the reverse transcription-polymerase chain reaction method with human platelet mRNA as template. These cDNAs were stably expressed in the Chinese hamster fibroblast cell line V79 and their substrate specificities towards known sulfotransferase isoenzyme-selective compounds determined. The nucleotide and derived amino acid sequences of the monoamine-sulfating form were identical to those previously identified in human liver and brain, but the cDNA for the human platelet phenol-sulfating form we isolated contained 5 and 2 amino acid changes from the two previously published sequences from human liver and brain, suggesting that we have identified a new allelic variant of human phenol-sulfating phenolsulfotransferase.