Outward movement of hemoglobin and K⁺ ion across rabbit erythrocyte membrane after heating, cooling and in acid medium was studied. One milliliter of rabbit blood was centrifuged and packed red cells were obtained. Packed red cells were resuspended by addition of 4 ml of 0.9% NaCl solution and were subjected to heating (57℃ for 5 minutes) or cooling (-4℃~-8℃ or -10℃~-11℃ for 10 minutes) For acid medium experiment packed ref cells were resuspended by addition of 4 ml of acid medium of PH 4.5 consisting of 0.01% glacial acetic acid in 0.85% NaCl solution and kept standing for 10 minutes. All red cell suspensions were centrifuged again and packed red cells were separated. This packed red cells were again suspended in 4 ml of NaCl solution of 0.8%, 0.7%, 0.6%, and 0.5% concentration respectively and kept standing for 20 minutes. The concentration of hemoglobin and K⁺ in the supernatant of the above red cell suspensions were measured and the following results were obtained. 1. Outward movement of hemoglobin and K⁺ was greatest in red cells subjected to heating. The movement paralled to the osmolal concentration gradient between extra- and intra-cellular phase of red cells. 2. In acid medium the outflux of hemoglobin and K⁺ increased as compared to the control. 3. In red cells subjected to the cold of -10℃~-11℃ the outflux of hemoglobin and K⁺ increased. Whereas in the environment of -4℃~-8℃ there was no change in the outflux of K⁺. The he-moglobin outflux showed rather a decreased as compared to tile control.