Hemin hemolysis of human erythrocytes at 37 degrees C has been investigated by the kinetic method. It has been observed that hemin affects erythrocytes by two mechanisms, inducing "quick" and "slow" hemolysis. The "quick" hemolysis is completed after the first few minutes. The final level of "quick" hemolysis is a function of relative hemin concentration. It is equal to zero when the latter is smaller than the minimum concentration Cmin = 10(8) molecules of added hemin per cell. The final level of "slow" hemolysis is always 100%. It is suggested that the limiting step of autohemolysis is the membrane proteins oxidation catalyzed by endogenous hemin originating from methaemoglobin during erythrocyte incubation at 37 degrees C.