Preeclampsia is one of the most frequent complications of pregnancy, however, little is known about its etiology. The objective of this study was to investigate the association of oxidized low-density lipoprotein ( oxLDL) and paraoxonase (PON1) activity in women with either preeclampsia or normotensive (NT) pregnancy. The study groups included 41 pregnant women with preeclampsia and 33 normotensive pregnant women. In all patients maternal serum total cholesterol (TC), high-density lipoprotein (HDL), low-density lipoprotein (LDL), and triglycerides (TGs) were measured using enzymatic methods. Serum PON1 activities and malondialdehyde (MDA) concentrations were measured by spectrophotometric methods, and oxLDL was measured by enzyme-linked immunoassay ( ELISA). Serum concentrations of lipid parameters ( TC, LDL, VLDL, and TGs) were significantly higher in preeclampsia compared with NT controls ( p < 0.001, p < 0.05, p < 0.05, and p < 0.001, respectively). Serum concentrations of MDA and oxLDL were significantly higher, while PON1 activity was significantly lower in preeclampsia compared with NT controls ( p < 0.001, p < 0.001, and p < 0.001, respectively). A positive correlation was detected between oxLDL and MDA ( r = 0.876), and a negative correlation was detected between both MDA and oxLDL and PON1 ( r = - 0.837 and r = - 0.759, respectively). Our data demonstrate that preeclampsia is associated with increased oxLDL and decreased PON1 activity. Elevated oxidative stress, oxLDL, dyslipidemia and decreased PON1 activities may cause vascular endothelial damage and contribute to the pathophysiology of preeclampsia. Copyright (C) 2005 S. Karger AG, Basel.