Although it has been reported previously that neurotropic MHV strains can spread within neurons in a retrograde direction, the molecular interactions mediating this spread have not been fully examined (6, 7) . In cultured neurons, viral interaction with the microtubule network in neuronal processes has been shown to be important; based on cross-interaction of antimicrotubule antibodies and the nucleocapsid protein (N), it is possible that such interactions might be involved in axonal transport mechanisms (15) . However, in view of the fact that the DM and NDM strains used in the present study differ only in spike protein and contain identical N proteins, our data suggest more of a role for the spike protein.