To define the clinical significance of plasma thrombomodulin (TM) values in elderly, we examined plasma TM in healthy young subjects, healthy elderly subjects and patients with cerebral infarction sequelae. We also studied the relationship with effective renal plasma flow (ERPF) and with the liver's protein-production ability. The TM values of healthy elderly subjects were higher than those of healthy young subjects. There existed an inverse correlation between TM values and ERPF. Accordingly, high TM values might significantly influence renal arteriosclerosis. From the inverse correlation identified between TM and serum cholinesterase, it was estimated that high TM might appear in conjunction with the liver's protein production ability. Patients with cerebral infarction showed higher plasma TM values. It is thought that angiopathy has been maintained in patients as the anamnesis of cerebral infarction even though it occurred in the past. The TM values of patients with diabetes mellitus (DM) were higher than those without it. Moreover, the TM values of patients with DM complicated by retinopathy were higher than those uncomplicated by retinopathy. It is therefore estimated that increased TM might occur with angiopathy resulting from DM. A possibility thus exists that plasma TM could be utilized as one of the markers for endothelial injury.