Diagnostic methods employed in enterovirus laboratories are generally laborious, slow and expensive. This is largely because type-specific neutralization tests still play the major role in identification and diagnostic serology. In the companion paper we describe the derivation of monoclonal antibodies against epitopes of the VPI peptide which are shared by all of the enteroviruses tested to date, with the exception of hepatitis A virus. This study describes the application of one of these monoclonal antibodies in several research and diagnostic procedures, illustrating a special utility in a wide variety of assay systems. This monoclonal antibody has proved particularly useful in the detection of enterovirus antigens in circulating immune complexes, and in identifying field isolates of this group of viruses. Immunohistochemistry, previously almost impossible in enterovirus diagnosis and research due to the large number of serotypes, is now shown to be practical and informative when this monoclonal antibody is used.