[en] Radioprotective capacity of bone marrow CFUs of adult thymectomized mice was studied. Lethaly irradiated mice were inoculated with bone marrow of mice thymectomized 8-11 months before. The colony forming capacity and proliferative rate of CFUs were studied 1-7.5 months after obtaining the radiation chimeras. It has been shown that proliferative capacity of bone marrow of adult thymectomized mice was reduced in comparison with that of normal animals. We also found that the content of CFUs in bone of those chimeras was reduced later - after 7.5 months. In this period (1-7.5 months) the cellularity of bone marrow did not change