The purpose of this study was to determine if plasma thrombomodulin levels, a glycoprotein found on the surface of the endothelial cell, are elevated in pregnant women with mild preeclampsia and if these levels correlated with other features of disease severity. Parameters were compared in three groups of women: (I) 30 pregnant women with mild preeclampsia, (II) 30 normotensive pregnant women of similar lengths of gestation, and (III) 30 normotensive healthy young women. Thrombomodulin levels were significantly elevated in women with preeclampsia as compared with those of gestation-matched pregnant and non-pregnant controls. There was no correlation between plasma thrombomodulin levels and creatinine and uric acid blood levels. It is thus suggested that plasma thrombomodulin levels are elevated in preeclampsia, even in its mild stage, reflecting a vascular endothelial damage.