Objective: Altered production of nitric oxide by the vascular endothelium may influence the pathogenesis of preeclampsia. The aim of this study was to measure circulating levels of nitric oxide metabolites (nitrites) in the uteroplacental, fetoplacental, and peripheral circulation of preeclamptic pregnancies compared with normotensive controls. Methods: Fifteen women with preeclampsia were compared with 16 women with normotensive pregnancies. At cesarean, blood samples were taken from the uterine vein draining the placental site, the umbilical vein, and the antecubital vein after delivery of the baby but before delivery of the placenta. Plasma nitrites were measured using the Greiss reaction after conversion of plasma nitrates to nitrites using nitrate reductase. Results: Nitric oxide metabolites were higher in the uteroplacental (P < .01), fetoplacental (P < .001), and peripheral (P < .02) circulations in samples from preeclamptic pregnancies compared with control pregnancies. In samples from the fetoplacental circulation only, nitric oxide metabolite levels were negatively correlated with gestational age (r = −.489, P < .01) and birth weight (r = −.544, P < .004). Nitric oxide metabolite levels were not significantly correlated with blood pressure, placental weight, or maternal age. Conclusion: In established preeclampsia, production of nitric oxide was higher in the uteroplacental, fetoplacental, and peripheral circulation than in normotensive pregnancies. This increase may be part of a compensatory mechanism to offset the pathologic effects of preeclampsia.