Paraoxonase is a high density lipoprotein-associated anti-oxidant enzyme. The aim of this study was to investigate the serum paraoxonase and arylesterase activities and associations between these enzymes and lipid hydroperoxide (LOOH) in preeclamptic patients.The study included 47 preeclamptic (25 severe and 22 mild preeclampsia cases) and 20 normotensive healthy pregnant women. Serum paraoxonase and arylesterase activities and LOOH levels were measured.While serum paraoxonase and arylesterase activities were significantly lower in both severe and mild preeclamptic patients (P<0.05 for both) than those in normal pregnant subjects, LOOH levels were significantly higher in severe (P<0.01) and mild preeclampsia cases (P<0.05) than in normotensive pregnant subjects. When all subjects were evaluated, there was a negative correlation between paraoxonase and LOOH (r=-0.24, P<0.05) and between arylesterase and LOOH (r=-0.31, P<0.01).Our results show that serum paraoxonase and arylesterase activities decrease in preeclampsia, and this situation may be associated with increased LOOH in these patients.