The direction of neural cell migration in relation to the pattern of alignment of adjacent radial glial fibers has been studied in the developing neopallium of embryonic days 16-18 mouse embryos. The radial glial fibers were stained with RC2, a monoclonal antibody selective for cells of astroglial lineage in the developing murine brain. Migrating neural cells were stained histochemically with 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal) following retroviral transduction of the gene encoding beta-galactosidase into proliferating progenitors on E13. The leading processes and, generally, the somata of migrating neurons were found to be aligned in parallel with the radial glial fibers, despite substantial variations in the patterns of alignment of the fiber fascicles. The set of observations is consistent with the hypothesis that neural cell migration is supported by radial glial fibers.