There were no changes of electrophoretic mobility (EPM) and ,32,P-incorporation rate in rabbit and rat erythrocytes 2 and 4 hrs after the irradiation of erythrocytes in vitro at 37℃ by γ-rays with doses of 250, 1000, 3000 and 5000 rad.,However, the cell EPM decreased and the ,32,P-incorporation rate increased markedly 2 and 4 hrs after the total irradiation of rabbits or rats with 600 rad.,The plasma taken from rabbits 2 and 4 hrs after irradiation could induce the similar changes in normal rabbit erythrocytes. Such activity of plasma from irradiated rabbit was preserved after inactivation by 56℃ for 15 min. cAMP level in rabbit plasma 2 and 4 hrs after irradiation increased and recovered to normal in 24 hrs.