Effects of pretreatment of mouse with low doses of internally deposited ¹⁴⁷Pm on the mutagenicity of both the bone marrow lymphocytes and the spermato-blasts induced by subsequent high dose of internally deposited ¹⁴⁷Pm were studied. Kunming male mice were injected from the tail vein with low doses of ¹⁴⁷Pm(NO₃)₃ of 0.37, 3.7 and 37 Bq/g body weight. Three days later the mice were injected with a high dose of ¹⁴⁷Pm(NO₃)₃ of 18.5 kBq/g body weight. The animals were sacrificed at 24 h after the high dose injection. The results show that the bone marrow lymphocytes and the spermatoblasts pre-exposed in vivo to low doses of ¹⁴⁷Pm can produce an adaptive response. The radioadapted cells had a resistance to the mutagenicity induced by the subsequent high dose of ¹⁴⁷Pm, that is, the proportion of both the bone marrow lymphocytes containing micronuclei and the sperm shape abnormalities was significantly lower than those for the pure high dose group (P < 0.01). In addition, the induction of the adaptive response of the cells possesses the different dose ranges for the different biological parameters. The ¹⁴⁷Pm dose ranges of the adaptive response are 0.37~3.7 and 0.37~37 Bq/g body weight for the frequency of micronucleated bone marrow lymphocytes and abnormal sperms, respectively.