Sulindac was administered as a single 300‐mg oral dose to six patients with end‐stage renal failure and six normal subjects. Plasma concentrations of sulindac and its sulfide and sulfone metabolites were examined over a 48‐hour period. As determined by ultrafiltration methods at 37°C, the percentage free of sulindac and sulindac sulfide in plasma was greater, respectively, in the patients with renal failure (10.50 ± 2.42 and 9.96 ± 1.21) than in the normal subjects (6.78 ± 0.45 and 6.01 ± 0.37). Free sulindac plasma concentrations were not different between the two groups. However, sulindac sulfide, total and free, plasma concentrations were substantially decreased in the group with renal failure. Total area under the curve (AUC) of the sulfide metabolite was 18% in the normal subjects and the free AUC was 29%. In patients with renal failure, the apparent half‐lives of sulindac (1.98 ± 0.76 hours) and sulindac sulfide (15.6 ± 5.8 hours) were not different from those of normal subjects. Sulindac sulfone half‐life was highly variable and longer in the patient group. Studies of dialysis clearance showed that sulindac and its metabolites are poorly dialyzed. A 4‐hour dialysis period increased the plasma binding of both sulindac and sulindac sulfide in the patient group. Based on the decreased plasma concentration of the active sulindac sulfide metabolite in the patient group, dosage adjustments may be required in patients with end