Dehydroepiandrosterone sulphate (DH AS) was administered intravenously to 70 women in the third trimester of pregnancy. By measuring the increase in the concentrations of estrogens in maternal plasma, it was hoped to assess the reserve capacity of the placenta. In normal pregnancies, umonjugated estradiol invariably showed a marked increase within 60 minutes of the injection of DHAS, reaching 174 to 478% above basal levels. Changes in unconjugated estrone were more variable, but significant increases usually occurred 2 to 3 hours after the peak concentration of estradiol. The concentrations of onconjugated estriol showed no significant change. Patients with preeclampsia, essential hypertension, retarded intrauterine growth, diabetes, and twin pregnancies did not show any major differences in response compared to the normal pregnancies. Two patients with intrauterine deaths had low basal concentrations of estrogens but responded to the DHAS injection by having significantly increased concentrations of unconjugated estradiol after 60 minutes. The only patient who did not show any increase in unconjugated estradiol levels after DHAS was thought to have a placental sulphatase deficiency. This test does not appear to have any advantage over existing methods of assessing the endocrine function of the placenta except in confirmation of placental sulphatase deficiency.