An adenovirus vector AxCALNFasL was constructed in order to transduce a gene for rat Fas-ligand, requiring co-expression of Cre recombinase for its expression. In the cosmid cassette, pAxCALNFasL, a stuffer DNA fragment flanked with two loxP sequences was placed between the promoter and Fas-ligand cDNA to prevent its expression in transfected 293 cells. COS-7 cells infected with AxCALNFasL alone did not induce apoptosis in cocultivated Jurkat cells, but the cells treated with AxCALNFasL and AxCANCre (an adenovirus expressing Cre recombinase with the CAG promoter) did. BALB/c mice injected with 10(9) plaque-forming units of AxCALNFasL and with different doses of AxCANCre, developed lethal acute liver failure. The number of the apoptotic hepatocytes increased dramatically with increased doses of injected AxCANCre, indicating that the level of transgene expression in the rodent liver appeared to be adjustable. Based on these observations, we conclude that vectors expressing a gene to produce cytotoxic substances can be constructed by the use of a Cre-mediated switching system. Our system also demonstrated that efficient expression of the toxic gene in the rodent liver was achievable by co-infection of adenovirus vectors carrying the target gene and Cre recombinase.