The effects of oral sulindac on renal hemodynamics were studied in normal subjects, elderly persons with mild renal failure, and patients with chronic renal disease. Renal function was measured before dosing and 24 hours and 28 days after oral sulindac. Effective renal plasma flow was reduced in all subjects after 24 hours. Effective renal plasma flow and the glomerular filtration rate were not altered after 28 days in control subjects, whereas effective renal plasma flow, but not glomerular filtration rate, was lower after 1 month in subjects with renal disease. None of these changes are likely to be of major clinical significance.