In order to study the possible role of nitric oxide (NO) in the human placenta, we measured the concentration of its stable metabolite nitrite (NO2-) in the placentas of women with normal pregnancies and those from pregnancies complicated by intrauterine growth restriction (IUGR) with or without fetal hypoxia. We have measured nitrites by the Griess reaction in 15 placentas from IUGR pregnancies and 12 controls. Cerebroumbilical ratio (C:U) was recorded by color Doppler ultrasound and values below 1 were considered to be a predictor for fetal hypoxia. NO2- levels measured in pathological placentas were increased for at least 93% as compared to control. Subjects from pregnancies complicated by IUGR and fetal hypoxia had increased NO2- as compared to the placentas from pregnancies with IUGR and normal fetal oxygenation. NO production in placenta is increased in pregnancies with IUGR. This effect is more pronounced in those with compromised fetal oxygenation.