[en] In order to compare the cell transformation induced by α- and γ-irradiation, primary cultures of tracheal epithelial cells from two rat strains, Sprague Dawley (SD) and Wistar Furth/FIsher F344 (WF/Fi) rats, were irradiated with ²⁴¹Am α-particles or ⁶⁰Co γ-rays. The relative transformation frequency (RTF) for WF/Fi primary cells was very close to the level of the spontaneous incidence and independent on the two irradiation types used. On the contrary, the RTF for the SD primary cells increased with a decrease of the LET radiation when the relative survival was higher than about 40%. Therefore, the RTF values reached 4-5 for α-particles and 10-12 for γ-rays. The RTF can be related to the intrinsic radiosensitivity of the rat epithelial cells. However, the difference in the radiation-induced RTF for SD or WF/Fi primary cells seems to be due to the development, under genetic control, of the initial lesion to the neoplastic state. (author)