1. Normal male subjects were given a rapid infusion of 3 litres of sodium chloride solution (150 mmol/l) with or without pretreatment with indomethacin.
2. There was marked individual variability in the rate at which the infused sodium chloride solution was subsequently excreted which was not related to the urinary sodium excretion in the previous 24 h.
3. There was no relationship between urinary prostaglandin E excretion during the 24 h preceding the sodium chloride infusion and the rate at which different individuals subsequently excreted sodium and water.
4. Renal plasma flow was significantly higher during the sodium chloride infusion than in the post-infusion recovery period, both with and without pretreatment with indomethacin, although it was significantly lower during each period in subjects pretreated with indomethacin.
5. Urinary prostaglandin E excretion was significantly decreased after the infusion of sodium chloride solution.
6. Indomethacin slightly decreased the rate of excretion of sodium and water.
7. Prostaglandins have a role in, but are not the main determinants of, the excretion of an intravenous infusion of sodium chloride.
8. The results do not support the suggestion that prostaglandin E produced within the kidney, as indicated by urinary prostaglandin E excretion, exerts a natriuretic action.