To investigate whether or not lactic acid inhibits the renal transport of oxypurines and oxypurinol, we administered physiological saline containing 0.2 mol sodium lactate to 5 normal subjects intravenously. Lactate infusion decreased the fractional clearance of uric acid, but the fractional clearances of hypoxanthine, xanthine and oxypurinol were not affected. These results suggest that uric acid and lactic acid share the renal transport system of organic acids but hypoxanthine, xanthine and oxypurinol do not. It is further suggested that allopurinol treatment is reasonable in subjects with hyperuricemia accompanied by hyperlactatemia since only the urinary excretion of uric acid and not oxypurines (hypoxanthine and xanthine) was inhibited by lactate infusion.