In diabetes, the serum uric acid level is low due to increased urate clearance; however, its mechanism remains unknown. We examined seven maturity-onset diabetic patients with rarely reported hypouricemia due to renal tubular abnormality to better understand the renal handling of urate by the diabetic kidney. The results of studies indicate that the increase in urate clearance was entirely accounted for by increased pyrazinamide-suppressible urate clearance. The maximal uricosuric response to probenecid administration was exaggerated. The effects of drugs on urate clearance were similar to those we have previously reported in the syndrome of inappropriate secretion of antidiuretic hormone. In four patients, the family survey did not reveal anyone with hypouricemia. These observations suggest that hypouricemia due to hyperuricosuria, which responds markedly to pyrazinamide and probenecid, is actually an indicator of renal tubular abnormality in diabetics.