Résumé : UV irradiation of simian virus 40 (SV40)-transformed human and hamster cells induced them both to express a mutator phenotype and to produce SV40. The mutator could also be activated indirectly by transfecting unirradiated cells with UV-damaged calf thymus DNA. In contrast, UV-damaged exogenous DNA failed to rescue SV40 from unirradiated transformed cells. These results suggest that the expression of transforming viruses and of cellular mutator functions is regulated by at least partially independent mechanisms. Unlike the activation of a cellular mutator phenotype, the rescue of SV40 from virus-transformed mammalian cells by UV light might require that the integrated viral DNA and/or specific cellular sequences are directly damaged. © 1985.