Pyrazinamide and probenecid tests were used to study the renal mechanisms for urate excretion in 10 normal subjects in the state of low serum uric acid levels (below 3.5 mg/dl), normal serum urate concentrations (between 3.6 and 6.4 mg/dl) and high serum uric acid levels (above 6.5 mg/dl). Presecretory reabsorption of urate was above 99% in all three conditions of uricemia, indicating that filtered urate is nearly completely reabsorbed in the proximal tubule regardless of serum uric acid concentrations. Urate secretion was significantly higher and postsecretory reabsorption was significantly lower when serum uric acid was raised than when serum urate levels were normal or low. The findings indicate that both urate secretion and postsecretory reabsorption play a role in urate homeostasis in states of hyperuricemia.