Angiotensin blockade was established in hypertensive patients with the competitive inhibitor saralasin and the blood pressure response was compared to prior renin determinations. Two patients with subsequently confirmed renovascular hypertension had normal peripheral renin and non-lateralizing renal vein renin ratios, yet both showed a clear-cut lowering of blood pressure after administration of the blocking agent, indicating the presence of renin-mediated hypertension. Thus, direct in vivo testing with saralasin appears to offer certain advantages over renin determinations.