The "effective" contribution of angiotensin II in blood pressure regulation was investigated in 6 patients on maintenance hemodialysis who were hypertensive at the time of the study (MAP 133 +/- 5 mmHg). Saralasin, a specific angiotensin II inhibitor, was infused at 0.5 and 2.5 microgram/kg/mn three hours before andone hour after hemodialysis. Before hemodialysis, a mean arterial pressure decrease of 13.2 to 19 p. 100 was obtained in 5 patients, arterial pressure being normalized in three of them. After hemodialysis, saralasin induced a normalization of arterial pressure in these 5 subjects. One patient, who was resistant to the saralasin infusion before and after the hemodialysis procedure, can be considered as purely volume-dependent. The renin-angiotensin system is probably one of the primary determinant of dialysis-resistant hypertension. However, a negative response to saralasin should encourage to control hypertension by more vigorous ultrafiltration during dialysis.