Further studies in the Heiligenberger strain suggested that, in that strain, the development of a genomic instability as well as the rate of developmental defects were transmitted to the next mouse generation after radiation exposure of the zygotes. Moreover, females that had been irradiated in utero showed a significant decrease of fertility. These effects were observed after X-irradiation of the zygotes with 1Gy [10,11]. The main goal of the experiments reported here was to investigate whether similar non-targeted effects could be observed in the next generation following irradiation of zygotes of two other radiosensitive strains, the CF1 and ICR, with much lower doses of X-rays (0.2 and 0.4 Gy). The lowest dose used in the present study still remained relatively higher than the maximumdose (about 0.08 Gy) to which embryos could be exposed in the case of pelvic CT procedures [12].