[en] The influence of dose rate on the dominant lethality in spermatogonia of mice was investigated. The comparison was made between the effects of chronic irradiation with 0, 300, 500, 1000 or 1500 rads at 0,01 rad/min and acute exposure with the same total doses at 25 or 150 rads/min respectively. After acute irradiation, the dominant lethality, revealed by the number of live embryos/1pregnant female, increased from 0% after 300 rads to 26%after 1500 rads. Post-implantation loss increased up to 500 rads and then remained on the same level after the higher doses. Chronic irradiation with 0,01 rad.min did not induce the dominant lethality regardless the accumulated dose. (author)