We present 2 patients associated with hypouricemia. Serum uric acid levels were 1.6 and 1.3 mg/l00 ml, and the ratios of urate clearance to creatinine clearance were 34.1 and 39.4%, respectively, while glomerular filtration rates (GFR) were normal. In the pyrazinamide (PZA) suppression test these 2 patients showed a different response of urate excretion. In the first patient urate excretion showed only a slight decrease following PZA. The load of benzbromarone did not increase urate excretion significantly. This patient is considered to have a defect of urate reabsorption in the proximal tubule, resulting in renal uricosuria. The second patient, on the contrary, showed nearly complete suppression of urate excretion after PZA. Uricosuric response to benzbromarone was far less than in the normal subjects. The suppression rate of urate excretion following PZA in benzbromarone-induced uricosuria was similar to the value of the normals. These results suggest that the latter has a defect of postsecretory reabsorption of urate in the tubule.