The time of half-elimination (T sub 50) of the toxic effects of cystamine is compared in irradiated and nonirradiated mice. The residual dose of cystamine three hours following administration of the preparation based on the change in the protector LD50 was calculated. With prophylactic use of cystamine, gamma irradiation at a dose of 850 r led to an increase in sub 50 from 1.8 (1.6 - 2.0) hours in intact mice to 2.3 (2.0 2.6) hours in irradiated animals. Three hours after preparation was used, the residual dose of cystamine was 44.2% in the irradiated mice and 24.5% of the original value in the nonirradiated animals. It is suggested that lengthening the elimination time of the toxic effect of cystamine under the influence of radiation is due to the decrease in the protector metabolism intensity under these conditions.