The surface topology and sequence conservation of different picornaviruses have been compared using molecular graphics and statistical analyses. The comparisons suggest that the canyons, surface depressions encircling the fivefold axes, are the sites of receptor attachment of enteroviruses as well as human rhinovirus (HRV). In HRV14, the receptor binding footprint extends beyond the canyon (Olson et al. (1993), Proc. Natl. Acad. Sci. USA 90, 507-511), but these more exposed regions are not conserved in polioviruses or minor receptor group rhinoviruses, suggesting some differences in receptor binding. When rhinoviruses are compared to other picorna- and parvoviruses, the surface sequence similarity relative to the similarity of buried residues is about the same. Thus, the effect of host immune surveillance on surface residues is similar. Therefore, it is probable that some means of protecting a conserved binding site from immune detection (such as a canyon) will be an essential requirement in other viruses. However, there may be other strategies for achieving this result. For instance, as in foot-and-mouth disease virus, the receptor attachment site of Mengo virus is associated with a flexible structural component which may inhibit the production of neutralizing antibodies that are able to recognize only one explicit conformation.