$^{86}Rb$ uptake of some organs and tissues, ego both lungs, both renal cortices. small intestine, liver and skeletal muscle were studied in the control and the rabbit subjected to pneumothorax. $^{86}Rb$ in the form of chloride mixed with physiological saline was intravenously. injected. The doses were $100{mu}c$ for a rabbit. The rabbits were sacrificed at intervals of 10, 20, 40, and 60 seconds after the injection of $^{86}Rb$, by the injection of saturated KCI solution. After sacrification, the organ and tissue sample were quickly removed. $^{86}Rb$ uptake in gm of the organs and tissues were measured. On the basis of uptake value, administered doses and body weight, % dose/gm tissues per 200 gm body weight was calculated. Followings were the results; 1. Pneumothorax resulted in a marked elevation in $^{86}Rb$ uptake value of collapsed lung and returned to normal level lately. 2. Contralateral lung of pnemothorax also showed marked elevation in $^{86}Rb$ uptake value and recovered to normal level. 3. Initial $^{86}Rb$ uptake value of liver, small intestine of the rabbit with pneumothorax showed some elevation as compared to control, but that of late stage were similar with control. 4. Local blood flow determination by means of $^{86}Rb$ uptake were inadequate in the collapsed lung of pneumothorax. 5. It was suggested that the mechanism for the initial elevation of $^{86}Rb$ uptake value in each organs and tissue were different from each other.