To determine whether the plasma level of uridine can be used to identify patients with gout, the plasma concentration of uridine was determined in patients with gout and normal subjects. Plasma uridine was significantly higher in patients with gout than in normal subjects. It was also significantly higher in patients with gout of the overexcretion (of uric acid) type than in those with gout of the underexcretion type. Plasma uridine was used to classify gout patients into underexcretion and overexcretion types, with a diagnostic accuracy of 92.5%. Results indicate that the plasma uridine concentration may be a marker of uric acid production and can be used to separate hyperuricemia into the overexcretion and underexcretion types.