The purpose of the present study is to ascertain comparative retention of fission fragment ,147,Pm in regenerated and fetal liver on induction, of chromosome aberrations in these cells. The results indicated that retention of ,147,Pm in regenerated liver was about 700 times than in fetal liver. The cumulative absorption dose in regenerated liver was about 2.87Gy, while in fetal liver — only 0.004 Gy. Under the same conditions, the incidence rate of chromosome aberrations in regenerated liver cells induced by ,147,Pm was 50.2%, and in fetal liver cells — about 28.3%. It should be concluded that the radiosensitivity to ,147,Pm was not uniform among the regenerated and fetal liver cells. Our study suggested that fetal liver cells show to be more radiosensitive to ,147,Pm than regenerated liver cells. Among the type of aberrations in both cells induced by ,147,Pm, chromatid breakages were predominant, accompanied with a few chromosome breakages.