Transplantation of hepatocytes from CBA/Cne mice into the fat pads of isogeneic recipients has been used for the quantitative in vivo study of cell survival and risk of transformation after x-ray irradiation (1-7 Gy). A survival curve for liver cells was generated in vivo with a D0 of 3.08 Gy and an extrapolation number not significantly different from 1. Data on liver tumor incidence in whole-body irradiated CBA/Cne and C57BL/Cne X C3H/HeCne (BC3F1) mice are also reported. A statistical analysis of trend in both cases proved a significant induction of tumors by x-rays mainly for doses above 2 Gy. The risk of transformation per surviving cell was estimated for both mouse strains. For CBA mice the data points suggested the presence of a linear component in the dose-effect curve at low doses, whereas for BC3F1 mice a quadratic expression appeared to provide a better description of the points from 1 to 6 Gy. The data of this study suggested that liver tumors can be induced by radiation in mouse strains with either a high or low spontaneous hepatoma incidence.