Using a competitive protein binding method, plasma deoxycorticosterone (DOC) was measured in 43 pregnant women. Elevated levels were first detected at 23–24 weeks and peak values were found near term. Mixed cord plasma DOC levels were significantly higher than maternal levels at the time of delivery, suggesting that the feto-placental unit was the source of the elevated maternal DOC. Suppression of maternal pituitaryadrenal axis with dexamethasone did not lower maternal plasma DOC levels. Following delivery both maternal and newborn plasma DOC rapidly fell, reaching normal adult levels within 24–30 hr. An umbilical arterial-venous gradient of plasma DOC at the time of birth was not found, suggesting that the fetal adrenal itself was not the sole source of the DOC arising from the feto-placental unit. Maternal plasma DOC levels of 7 women with toxemia of pregnancy during the third trimester were not significantly different from levels found in women with normal pregnancies of similar duration.