We have reported the production of monoclonal antibody 4C5, which recognizes a cell surface antigen, the 4C5 antigen, involved in granule cell migration processes. In the present study, we investigated in a more precise manner the role of the 4C5 antigen in the different types of granule cell migrations that take place during cerebellar development. When cerebellar explant cultures derived from 10-day-old rats were performed for 2 days in the presence of monoclonal antibody 4C5, vertical granule cell migration, occurring in the presence of glia, was not significantly inhibited. In contrast, when monoclonal antibody 4C5 was included in the medium of microexplant cultures derived from 4-day-old mice and maintained for 4 days in vitro, granule cell migrations that occurred both parallel and perpendicular to the neurite bundles that were free of glia were inhibited. Moreover, a stronger inhibitory effect of the antibody was observed on migration perpendicular to the neurite bundles compared with the parallel type of migration. Our results indicate that the 4C5 antigen differentially affects the different developmental stages and types of granule cell migration during rodent cerebellar development.