Concentrations of thrombomodulin in blood plasma were measured by a one-step sandwich enzyme immunoassay (EIA). The concentrations in normal healthy subjects were 9.9 +/- 2.9 ng/ml. The concentrations were found to be significantly higher in patients with SLE, RA and other collagen diseases in their active stages than at their non-active stages. The concentrations increased in patients with DIC, and significantly higher levels were observed when DIC was complicated by multiple organ failure. These findings indicate that plasma concentrations of thrombomodulin may be a useful parameter for vascular injuries caused by inflammatory processes or coagulation/fibrinolysis reactions.