A pregnancy with placental sulfatase deficiency was suspected when a 36-year-old patient at 41 weeks of gestation was found to have extremely low urinary estriol excretion and an otherwise normal prenatal course. The maternal plasma levels of estriol and estradiol 17-beta (E2) were extremely low and estetrol (E4) was undetectable (less than 40 pg/ml), whereas dehydroepiandrosterone sulfate (DS) was normal. THE AMNIOTIC Fluid DS concentration was 22-fold higher than the mean of normal pregnancy, while that of dehydroepiandrosterone (D) and androstenedione (A) was normal. Following intravenous infusion of 50 mg DS, no rise of plasma E2 was noted and plasma E4 levels remained undetectable. At 42 weeks of pregnancy, after induction of labor failed, a healthy male infant was delivered by cesarean section. The umbilical vein (UV) and umbilical artery (UA) levels of DS were extremely high, and those of E2 and E4 were subnormal. The UA level of A was normal and the levels of D and testosterone were slightly elevated. In vitro studies of placental microsomes and the 10,000 x g supernantant confirmed the diagnosis of placental sulfatase deficiency. The infant at 6 months of age had normal growth and development and normal peripheral plasma DS concentration.