Nucleotide sequencing and phylogenetic analysis of 10 recognized prototype strains of the porcine enterovirus (PEV) cytopathic effect (CPE) group I reveals a close relationship of the viral genomes to the previously sequenced strain F65, supporting the concept of a reclassification of this virus group into a new picornavirus genus. Also, nucleotide sequences of the polyprotein-encoding genome region or the P1 region of 28 historic strains and recent field isolates were determined. The data suggest that several closely related but antigenically and molecular distinct serotypes constitute one species within the proposed genus Teschovirus. Based on sequence data and serological data, we propose a new serotype with strain Dresden as prototype. This hitherto unrecognized serotype is closely related to porcine teschovirus 1 (PTV-1, former PEV-1), but induces type-specific neutralizing antibodies. Sequencing of field isolates collected from animals presenting with neurological disorders prove that other serotypes than PTV-1 may also cause polioencephalomyelitis of swine.