1. Acute renal failure was induced in conscious rats by subcutaneous injection of glycerol.
2. Expansion of the extracellular space by infusion of 150 mmol/l sodium chloride (saline) partly protected the animals against acute renal failure.
3. This protective effect of saline infusion disappeared when the animals were treated with indomethacin. This effect could be reversed by the addition of prostaglandin (PGE2) to the saline infusion.
4. We suggest that prostaglandins may be involved in mediating the protection afforded by saline infusion against acute renal failure due to glycerol.