The effects of 2 days of oral dosing with sulindac (200 mg twice a day) or indomethacin (75 mg twice a day) on glomerular filtration rate, urinary excretion of prostaglandin E2, sodium homeostasis, and other renal function parameters were investigated in eight patients with chronic stable impaired renal function. Indomethacin reduced creatinine clearance (from 41.0 +/- 7.9 to 30.3 +/- 6.3 ml/min) and increased serum levels of creatinine and beta 2-microglobulin. Sulindac had no effect on any of these parameters. Both drugs induced depression of urinary prostaglandin E2 excretion; this depression was greater after indomethacin. Urinary sodium excretion fell from 144.4 +/- 18.7 to 85.5 +/- 9.7 mmol/24 hr after indomethacin and from 131.7 +/- 11.6 to 103.4 +/- 13.3 mmol/24 hr after sulindac. Body weight increased 1.2 kg after indomethacin but was not changed by sulindac. Plasma renin activity was reduced from 2.3 +/- 0.8 to 1.7 +/- 0.6 nmol/L/hr by sulindac and from 2.8 +/- 0.8 to 1.5 +/- 0.5 nmol/L/hr by indomethacin. Urinary N-acetyl-beta-glucosaminidase and kallikrein excretion was not changed by either drug. Our data suggest that sulindac affects renal prostaglandin E2 synthesis and sodium excretion in patients with severe renal failure to a lesser extent than does indomethacin. Sulindac still seems to be the drug of choice in this group of patients, but glomerular filtration rate, body weight, and electrolyte balance should be carefully monitored.