A simplified method for the local blood flow determination by means of 86Rb was developed in rats and rabbits. 86Rb in the form of chloride mixed with physiological saline was intravenously injected. The doses were 10μCi for rats and 100μCi for rabbits, which were injected in less than 5 seconds. The rats were sacrificed after 30 seconds, and the rabbits at the intervals of 10, 20, 40 and 60 seconds, by decapitation or rapid intravenous injection of 3 to 5ml of saturated KCL After bleeding, the organ and tissue samples, e.g. lungs, renal cortex, jejunum and skeletal muscIe were quickly removed. The 86Rb uptake in 1 gram of the organs and tissues were measured. On the basis of uptake value, administered dose and body weight, the local blood flow was calculated. Following were the results : 1.The uptake values of 86Rb in the above organs and tissues of rats were different from other previous reports, in which the large rats were used. It appears, therefore, that the cerrection on the basis of body weight is necessary. 2. The uptakes of 86Rb in the above organs and tissues of rabbits remained rather stationary within 20 to 40 seconds. 3. The local blood flow in the above organs and tissues were calculated from 86Rb uptake in per cent dose per I gram tissue for 200 gram body weight. The formula could be applied not only to the rabbits but to the rats. 4. The present method could be applied to tbe comparison of the local blood flow between the various organs and tissues of the control and experimental animals.