Experiments were conducted which revealed the renal transport mechanism(s) of oxypurines by employing uricosuric agents and pyrazinamide. All specimens being drawn from healthy, normal subjects, the data showed that probenecid increased fractional uric acid, fractional hypoxanthine and fractional xanthine clearance, 3.97-, 1.52- and 2.31-fold, respectively, while benzbromarone increased fractional uric acid clearance 2.11-fold, decreased fractional xanthine clearance 0.48-fold and had no effect on fractional hypoxanthine clearance. In addition, pyrazinamide decreased both fractional uric acid clearance 0.35-fold and fractional xanthine clearance 0.44-fold but increased fractional hypoxanthine clearance 1.49-fold. These results suggest the possibility of differing renal transport mechanisms among the purine bases, uric acid, hypoxanthine and xanthine.