The mechanism of uric acid transport in normal kidneys is describe dtogether with alterations in that mechanism that take place in chronic renal failure and are responsible for the increased uric acid excretion per nephron, as renal failure advances. The pyrazinamide suppression technique used to separate urate secretion from reabsorption is discussed together with the possibility for a hormonal origin for the renal adaptation for uric acidexcretion in renal failure.