Transgenic mice susceptible to poliovirus infection were produced by introducing a human gene encoding cellular receptors for poliovirus into the mouse genome. Expression of receptor mRNAs in tissues of the transgenic mice was analysed using Northern blot hybridization. The results indicate that the human gene is expressed in many tissues of the transgenic mice just as in human tissues, and that the amount of the receptor mRNAs varies from tissue to tissue. The transgenic mice inoculated with poliovirus by any of the routes tested in this study show clinical symptoms similar to those in humans and monkeys, although the sensitivity of the mice depended on the inoculation route. In any route, the virulent Mahoney strain of type 1 poliovirus is much more virulent than the attenuated Sabin 1 strain in the transgenic mice. These observations suggest that the transgenic mice become an excellent new animal model for studying molecular mechanisms of pathogenesis of poliovirus and for assessing oral poliovirus vaccines.