Preeclampsia has been associated with increased platelet activation detected before disease onset. Platelets are involved in hemostasis and also directly initiate an inflammatory response of the vessel wall. Inappropriate activation of platelets may be involved in pathogenesis in preeclampsia by promoting coagulation and thrombosis, and also as a mediator of inflammation. Platelets may release inflammatory mediators such as soluble CD40 ligand. The plasma level of soluble CD40 ligand was investigated during preeclamptic (n =20) and normal pregnancies (n = 20) to emphasize inflammatory response in preeclampsia. The mean soluble CD40 ligand levels were 1.08 +/- 0.43 ng/mL in patients with preeclampsia and 0.76 +/- 0.24 ng/mL in healthy pregnant women, which was statistically significant (P =. 01). To clarify whether inflammation may cause inappropriate endothelial cell activation or inappropriate endothelial cell activation may start this inflammatory response, future studies are needed in a larger study population.