Plasma levels of thrombomodulin (TM), a glycoprotein found on the surface of the endothelial cells, are elevated in certain diseases that are characterized by damage to the vascular endothelium. Such damage is thought to be involved in preeclampsia. We therefore studied the plasma levels of this substance in 13 preeclamptic women as compared with 14 normal pregnant and 16 nonpregnant women. We found that the plasma levels of TM were significantly elevated in preeclamptic women vs. controls. A significant positive correlation was observed between the plasma TM level and that of serum creatinine. It is thus suggested that elevated TM levels in preeclampsia may reflect a decrease in renal clearance rather than vascular endothelial damage.