Two patients had hypouricemia due to increased uric acid clearance. Their daily urinary uric acid excretions were normal. In both patients, pyrazinamide decreased urinary uric acid clearance to almost while probenecid increased it markedly. No other renal tubular or metabolic abnormalities were found. The serum electrolytes and the urinary electrolytes excretions showed no abnormalities. It appears that increased secretion of uric acid in the renal tubule is most probably responsible for hypouricemia in these patients. This report adds to the list of hypouricemic conditions due to a new isolated renal tubular abnormality.