Abstract: The concentration of plasma immunoreative endothelin （ET）was measured in 30 old patients who Suffered from essential hypertension and were treated by conventional antihypertensive therapy. The blood ET concentration was also measured in 5 untreated hypertensive old patients and 14 healthy old men. The concentration of ET in the health elderly was the lowest, where as in the treated group, the higher the level of blood creatinine（Cr）, the higher the ET concentration. Furthermore, if the blood Cr concentration was similar, the concentration of ET in the untreated patients was higher tnan that of the treated cases. The results suggested thet the concentration of plasma ET were reiated to the serum Cr and blood pressure level in old patients with hypertension.