BACKGROUND We assessed plasma endothelin-1 (ET-1) concentrations in a group of hypertensive subjects in order to determine the possible presence of a disorder of ET-1 production and release. METHODS A selected cohort of hypertensive subjects was compared with a control group. Plasma levels of ET-1 in baseline conditions and after cold the pressor test (CPT) were measured. All subjects were studied as outpatients. Twenty-one male hypertensive patients were compared with 15 male controls. The hypertensive patients had undergone clinical examinations to rule out the presence of vascular damage. Clinical examination of the controls was performed to rule out hypertension. Patients with essential hypertension were 21 males, age: 57+/-7 years, body mass index 22.3+/-11.2 kg/m2. We assessed plasma ET-1 in baseline conditions and after a cold pressor test. RESULTS Means +/-SD baseline concentrations of ET-1 were 12.47+/-2.41 pg/ml in hypertensives and 8.2+/-3.8 pg/ml in controls (p<0.01). Mean +/-SD post CPT plasma ET-1 was 12.55+/-2.83 pg/ml in hypertensive subjects and 8.6+/-1.9 pg/ml in controls (p<0.01). CPT did not modify plasma ET-1 concentrations in either group. CPT significantly raised arterial pressure only in hypertensive subjects. CONCLUSIONS These results lead us to postulate the presence of a disorder of ET-1 production and release in hypertensive subjects.