Uric acid excretion can be measured in milligrams of urinary uric acid per decilitre of glomerular filtrate by obtaining the product of urinary uric acid and serum creatinine concentrations and dividing by the urine creatinine (all concentrations in mg/dL). In 29 normal adult men, the excretion rate in spot, midmorning samples was 0.4 +/- 0.1 (SD) mg of uric acid per decilitre of glomerular filtrate. Eight of 36 untreated gouty men excreted acid at a rate more than three standard deviations above normal. Excretion of uric acid is conveniently and physiologically assessed by this simple method.