The RGD sequence (Arg-Gly-Asp) is known to bind integrins and the synthetic RGD tripeptide inhibits cell adhesion and migration of cultured neuronal cells. However, it is not known whether migration of neuronal precursors in vivo during the cortical histogenesis of the mammalian telencephalon depends on the RGD sequence. To examine this possibility, the RGD peptide was injected into the telencephalic vesicle of mouse embryos. A hypoplastic cortical plate was induced and histological analysis and BrdU-immunohistochemistry revealed that the RGD sequence is involved in neuronal migration and proliferation in the telencephalon during formation of the cortical plate.