1. In rats deprived of food and water for 24 h acute renal failure was produced by the intramuscular injection of glycerol. Eight hours later plasma urea concentration had increased threefold despite a small rise in urine volume. Plasma concentrations of renin and renin substrate were elevated.
2. When saralasin, a competitive antagonist of angiotensin II, was infused for 8 h after glycerol injection, urine volume and plasma urea were similar to values in rats that had received an infusion of saline.
3. Administration of rat serum (4·5 ml h−1 kg−1) for 4 h suppressed plasma renin concentrations, but plasma urea increased to the same extent as in rats without serum.
4. When saralasin and serum were infused at the same time, urine volume, urine osmolality and solute excretion increased and the rise of plasma urea was diminished.
5. Saralasin has a protective effect against glycerol-induced acute renal failure only when volume is replaced concomitantly.