Endothelin-1 (ET-1) is a vasoconstrictor peptide derived from endothelium. Many authors have shown that ischemic stroke is associated with elevated plasma ET-1 levels. Also, the present findings related to plasma ET-1 levels with clinical status, size of the infarction, location of the infarction, and prognosis of the cerebral infarction were contradictory. In this study, plasma ET-1 levels in 30 patients with cerebral infarction within 72 hours after the onset of focal neurologic deficit and at their seventh day postinfarction were measured by a microplate enzyme immunoassay. Thirty sex- and age-matched healthy subjects were accepted as a control group. The mean plasma ET-1 concentrations in patients on admission, in patients at day 7, and in control subjects were 1.93 +/- 1.79, 1.03 +/- 1.02, and 0.65 +/- 032 fmol/mL, respectively. The mean plasma ET-1 level of patients on admission Was found to be significantly higher than in patients at day 7 and in control subjects (p < 0.05). No significant difference in ET-1 levels was observed between the patients at day 7 and control subjects. Furthermore, there was no correlation between plasma ET-1 concentration and size of infarction, location of infarction, degree of clinical neurologic deficit, or prognosis of cerebral infarction. It was concluded that plasma ET-1 levels shortly after ischemic stroke were increased, which may be associated with the acute-phase reaction of cerebral infarction and may have deleterious effects on development of neuronal injury.