We present evidence for the existence of a previously undescribed sulfotransferase isoenzyme in adult human liver which sulfates endogenous and xenobiotic estrogens (estrone and 17 alpha-ethinylestradiol). The enzyme was resolved from other sulfotransferases using anion exchange chromatography and further purified by gel filtration and affinity chromatography. Using antibodies against rat liver estrogen and hydroxysteroid sulfotransferases, it was shown that the adult human estrogen sulfotransferase has a subunit molecular weight of 33kDa, is immunologically related to its rat counterpart and also to the human phenolsulfotransferase enzyme family, but not to human hydroxysteroid sulfotransferase.