Sulfotransferase with 2-naphthol as substrate was investigated in the cytosolic fraction of human fetal liver, lungs, kidneys, adrenal glands, intestine and placenta and also in liver, lungs, kidneys, intestinal and urinary bladder mucosa from human adult subjects. All tissue specimens assayed catalyzed the sulfation of 2-naphthol at a significant rate. The activity (expressed as pmole per minute per milligram protein; mean +/- SD) was 211 +/- 197 (n = 46) fetal liver; 22 +/- 12 (n = 29) placenta; 625 +/- 205 (n = 42) human adult liver. In fetal kidneys (576 +/- 177; n = 6) and gut (558 +/- 293; n = 6) the activity was twice as high as in liver. In the lungs (273 +/- 125; n = 6) and in the adrenals (174 +/- 119; n = 19) the sulfotransferase activity was comparable with the hepatic one. In human adult extrahepatic tissues the highest activity was found in the intestinal mucosa (153 +/- 49; n = 4) and the lowest one in the urinary bladder mucosa (16 +/- 4; n = 4). This paper shows that the sulfotransferase has a wide distribution in the human fetus and the distribution pattern of this enzyme is different in the human fetus and adult subject.