The benzethonium chloride method of Iwata for the turbiditometric determination of minute amounts of protein reacted in alkali condition was improved for application to the measurement of urinary protein before and after physical loading. 1) In order to determine minute amounts of protein based on Iwata's method, an improved method was devised. A 0.2ml of urine was added to 3.9ml of a mixture of 33.85mol/l of EDTA 4Na and 0.5mol/l of NaOH. 2) The correlation coefficient of both modified Meulemans method and modified Iwata's one was R=0.96 and the regression equation was y=1.33x+0.17 where x was protein concentration obtained by modified Iwata's method using urine of students before Judo and basketball exercise. The correlation coefficient of both methods was R=0.98 and the regression equation was y=0.91x+0.27 using urine of students agter Judo and basketball exercise. The value obtained by both methods nearl coincided with each other. 3) Turbidity produced by modified Iwata's method was more stable after addition of reagents than that by modified Meulemans method. 4) A minute amount of urinary protein could be preserved and determined by modified Iwata's method up to 4days under freezing at -20℃.