In the present study, four new forms of aryl sulfotransferase cDNAs have been isolated and their structures determined. A compilation of primary structures of 16 different sulfotransferases, including enzymes metabolizing endogenous chemicals and xenobiotics, showed a considerable extent of similarity among bacterial, plant and mammalian species, and indicates that these enzymes constitute a supergene family. Aryl sulfotransferase and estrogen sulfotransferase are shown to belong to a single gene family (ST1) which consists of at least four subfamilies, whereas, based on the sequence similarity, hydroxysteroid sulfotransferases constitute a distinct family (ST2). Little or no clear similarity was observed between the primary structures of enzymes N-sulfating aminosugars and those sulfating hydrophobic chemicals such as phenols, alcohols or amines, indicating that both types of enzymes diverged early in their evolutionary history. Two regions in the C-terminal parts are, however, conserved among all enzymes examined, which suggests a possibly essential role of these sites for the binding of a PAPS cofactor or for sulfate transfer.