According to the four component theory, urate transport in nephrons consists of 4 steps, glomerular filtration (GF), presecretory reabsorption, secretion and postsecretary reabsorption. We have been investigating quantitatively the relationship among the steps of urate transport and urinary urate excretion (Uua) using the formulaUua = {Ccr (1 - R 1 ) + Cs} Sua (1 - R 2 )where Sua: serum urate level, Ccr: creatinine clearance representing the GF rate, R 1 : presecretory reabsorption rate, Cs: secretion rate, R 2 : postsecretory reabsorption rate. In 10 gouty patients with underexcretion and in 12 normal controls, Sua and Uua were determined before and after administration of various doses of pyrazinamides or benzbromarones. Using this formulas R 1 , Cs, R 2 were calculated as 1.004, 39.0, 0.889 for gouty patients and 0.996, 63.4, 0.885 for normal controls, respectively. Inspite of a marked decrease in Cs, amounts of urate secretion (Cs Sua) were only slightly reduced by the reduction in high Sua.In summary, Cs in the nephrons of gouty patients was significantly lower than that of normal controls, but R 1 and R 2 were almost equal in the two groups. The decrease in Cs was suspected of being the main cause of urate underexcretion in gouty patients.