Despite extensive investigations over the last decades, several aspects of the pathogenesis of enterovirus infections in humans and animals are only poorly understood, such as the molecular basis of virulence (in particular of neurovirulence), tissue tropisms (e.g. the precise site of initial virus replication in the human intestinal tract), and precipitating factors of paralytic disease ("disposition"). Studies on poliovirus myocarditis in man are reviewed. Unequivocal evidence on replication of poliovirus type 2 (strains MEF1 and Lansing) in newborn and suckling mice and on poliovirus myocarditis is presented. Our observations strengthen the thesis of similar pathogenic potentials of the enterovirus group.