A patient with asymptomatic adult Fanconi syndrome with glycosuria, amino-aciduria, hypophosphatemia, and renal tubular acidosis was found to have hypouricemia (serum uric acid, 1.5-1.8 mg/100 ml) secondary to increased renal clearance of urate (urate clearance/glomerular filtration rate, 32 per cent). Increased urate clearance in this patient with multiple reabsorptive defects probably represents diminished urate reabsorption. Consistent with this, the uricosuric response to probenecid was diminished. Reabsorption of filtered urate appeared to be intact. Inhibition of urate secretion with pyrazinamide completely suppressed the uricosuria in this patient, suggesting that increased urate clearance was due to either enhanced secretion or diminished reabsorption of secreted urate. There was no direct evidence for increased urate secretion. The response of urate excretion to pharmacologic inhibitors of tubular transport of urate differs in various clinical states associated with hyperuricosuria. The responses may reflect different mechanisms of hyperuricosuria.