Rapid carcinogenicity tests were done with transgenic (Tg) mice human prototype c-HRAS gene, namely BALB/cByJ x C57BL/6JF1-TgN(HRAS)2 or CB6F1-HRAS2 mice. The studies were conducted as the first step in the evaluation of the CB6F1-HRAS2 mouse as a model for the rapid carcinogenicity testing system. Results of short-term tests of various genotoxic carcinogens indicated that CB6F1-HRAS2 mice are more susceptible to these carcinogens than control non-Tg mice. According to the first-step evaluation studies, more rapid onset and a higher incidence of more malignant tumors can be expected with a higher probability after treatment with various genotoxic carcinogens in the CB6F1-HRAS2 mice than in control non-Tg mice. The CB6F1-HRAS2 mouse seems to be a promising candidate as an animal model for the development of a rapid carcinogenicity testing system.