N 13-b method for determination of uric acid by AutoAnalyzer- I was proposed from Technicon Corporation, but the sensitivity of this method was insufficient. According to the modification by Patel, good sensitivity was obtained for determining of uric acid, but insufficient separation between peaks was accompanied. To get good separation, Patel's method was reexamined by the authors, and the results were as follows. Sufficient separation was obtained by modifing the flow diagram of Patel's method. The mean recovery rates of uric acid added to serum and urine were 103.6% and 102.5%, and coefficients of variation were 1.27% and 1.05% respectively. The correlation between this modified Patel's method and the U.A. test Wako method was recognized (serum : n=95, r=0.97, urine : n=35, r =0.99). According to our modified method, uric acid concentration in serum of 68 subjects, were 5.8±0.9mg/100ml in 29 males and 4.4±0.8mg/100ml in 39 females.