In experiments with dogs exposed to 2.9 Gy (LD80/45) it was found that plasmapheresis treatment 4-6 h after irradiation reduce the severity of the radiation sickness clinical manifestations and post-radiation toxemia thus increasing the rate of animal survival up to 60%. Sham plasmapheresis included all the manipulations of plasmapheretic treatment except plasma substitution and had no detoxication effect and did not affect the irradiated animals survival. This is evidence for leading role of detoxication in the mechanisms of the therapeutic action of plasmapheresis in acute irradiation.