Ticrynafen, 125--250 mg/day was compared with probenecid 0.5--1.0 g/day in patients with elevated serum uric acid values in a randomized, double-blind crossover study. Each treatment period lasted 12 weeks. The mean reduction in serum uric acid from 9.4 +/- 1.2 to 6.22 +/- 1.2 mg/dl (33.8%) during ticrynafen was greater (p less than 0.01) than that from 9.46 +/- 1.1 to 7.0 +/- 1.3 mg/dl (26%) during probenecid treatment. There were slight increases in serum creatinine and BUN and decreases in body weight during ticrynafen treatment. There were no statistically significant changes in serum electrolytes. The hypouricemic effect of ticrynafen was well maintained during its subsequent open-label administration for 18 months without any deterioration of renal function.