Serum and 24-hour urinary phosphate levels in primary gout patients and control subjects were measured. About 45% of gouty patients showed mild hypophosphatemia. However, mean 24-hour urinary excretion of phosphate was significantly elevated as compared with that of controls. Gouty patients showed a significantly decreased tubular reabsorption of phosphate and renal phosphate threshold. It seems that tubular phosphate transport in gouty patients is impaired, and this is the major cause of hypophosphatemia.