To determine whether an increase in the plasma concentration of uric acid by sucrose intake is ascribable to enhanced purine degradation and/or decreased urinary excretion of uric acid, we measured the plasma concentrations of purine bases (uric acid, hypoxanthine, and xanthine) and uridine, as well as the urinary excretion of purine bases in 7 healthy subjects before and after administering sucrose at 1.5 g/kg of body weight in 2 related experiments, with and without an administration of 300 mg of allopurinol. In addition, in the control experiment without an administration of sugar and with an administration of 300 mg of allopurinol, we measured the same parameters in those 7 subjects. Without added allopurinol, sucrose increased the plasma concentration of uric acid by 11% (P<.01) as well as that of uridine, although it did not significantly increase the plasma concentrations of hypoxanthine and xanthine or the urinary excretion of uric acid. On the other hand, the plasma concentration and urinary excretion of hypoxanthine were increased by 2.4-fold (P<.05) and 3.42-fold (P<.05), respectively, and the plasma concentration of xanthine was increased by 1.2-fold (P<.05) together with an increase in the plasma concentration of uridine in the experiment with allopurinol administration. In contrast, the plasma concentration and urinary excretion of uric acid and the urinary excretion of xanthine were not increased. In addition, in the control experiment, all parameters did not change significantly. These results indicate that purine degradation enhanced by sucrose plays a major role in the increased plasma concentration of uric acid.