A clinical investigation was carried out on patients with uric acid stones in order to study the frequency and pathogenesis of uric acid nephrolithiasis. Of 652 patients with stones in the upper urinary tract in whom the stone composition could be examined, 36 patients and uric acid stones (5.5%). The male to female ratio was 11:1. The average age of the 33 male subjects was 49 +/- 11 years (mean +/- SD), and the 3 females were 22, 37 and 42 years old, respectively. Two of the females showed hypouricemia. With regard to stone composition, pure uric acid stones were present in 26 cases (72%), a mixed uric acid and calcium oxalate stones were found in 6 cases (17%), both pure uric acid and mixed uric acid and calcium oxalate stones were observed in 3 cases (8%), and a mixed uric acid and sodium acid urate stone in 1 (3%). Biochemical studies on male patients showed that the blood uric acid level was higher in the uric acid stone group and the pure uric acid stone group compared to the calcium stone group. The blood uric acid levels of the former 2 groups did not differ from the control group. With respect to urine chemistry, the excretion of calcium in the uric acid stone group was significantly lower than that in the control group. In the uric acid stone group and the pure uric acid stone group the excretion of calcium tended to be lower than that in the calcium stone group. The amounts of oxalic acid excreted in the uric acid stone group and in the pure uric acid stone group were low compared to the calcium stone group. Oxalic acid elimination in these 2 groups did not differ from the control group.(ABSTRACT TRUNCATED AT 250 WORDS)