Equine rhinoviruses (ERVs) are picornaviruses which cause a mild respiratory infection in horses. The illness resembles the common cold brought about by rhinoviruses in humans; however, the presence of a viraemia during ERV-1 infection, the occurrence of persistent infections and the physical properties are all more reminiscent of foot-and-mouth disease virus (FMDV). cDNA cloning and sequencing of the genomes of ERV-1 and ERV-2 between the poly(C) and poly(A) tracts showed that the serotypes are heterogeneous. Nevertheless, the genomic architecture of both serotypes is most similar to that of FMDV. Indeed, a comparison of the derived protein sequences of ERV-1 shows that their identity is greatest to FMDV. In contrast, most ERV-2 proteins are more related to encephalomyocarditis virus (EMCV) proteins than they are to FMDV or ERV-1. These results place ERV-1 alongside FMDV in the aphthovirus genus of the picornavirus family and indicate that this virus may serve as a model system for examining the biology of FMDV.