Background: Preeclampsia is characterized by vasospasm, multiple organ hypoperfusion and endothelial cell damage. Many of its signs and symptoms can be explained by an imbalance in the vasomotor tone-regulating factors, including nitric oxide (NO) and endothelin-1 (ET-1). Methods: Plasma samples of 59 women (20 healthy nonpregnant (NP), 20 normotensive pregnant (NTP) and 19 preeclamptic pregnant (PEP) women) were investigated by means of nitrite (NO2-)/nitrate (NO3-) (two end products of nitric oxide metabolism) and endothelin-1 values. Results: PEP, when compared with NP and NTP, showed a significant increase in the plasma nitrite/nitrate and endothelin-1 concentrations. There was a weak but significant correlation between the nitrite/nitrate and endothelin-1 concentrations in the NP and NTP groups (r(1) = 0.46, P < 0.05, and r(2) = 0.38, P < 0.05, respectively) which probably revealed the balance between these vasoactive factors. In PEP, no significant correlation between nitrite/nitrate and endothelin-1 was found. Increased nitric oxide production could be the compensation against the vasoconstriction and hypertension in preeclampsia. Conclusions: A lack of correlation between nitrite/nitrate and endothelin-1 probably indicates that in preeclampsia, a primary defense mechanism of the compensatory nitric oxide may be lost. (C) 2002 Elsevier Science B.V. All rights reserved.