Poliovirus is a member of the Picornaviridae family of viruses. Characteristic of all members of this family, the poliovirus genome consrsis of approx 7500 bp of RNA of the plus sense polarity (1,2). Poliovirus is undoubtedly one of the most thoroughly characterized animal viruses. The three-dimensional structure of the entire virion is known (3), an infectious cDNA clone of the poliovirus genome has been generated (4,5), the entire nucleic acid sequence of poliovirus has been determined (1), and the cellular receptor that pohovirus uses to enter cells has been cloned and sequenced (6). The availability of a transgenic mouse expressing the poliovirus receptor has facilitated further description of the pathogenesis of poliovirus (7,8).