The epigenetic factors involved in regulating the proliferation and differentiation of cells of the developing mammalian central nervous system are largely unknown. In this study, laminin, a molecule which is present in the basal lamina from the earliest stage of neural tube formation, has been examined in vitro for its possible regulatory role in mammalian neural development. Purified populations of murine neuroepithelial (NEP) cells isolated from the 10-day embryonic telencephalon and mesencephalon respond in vitro to laminin by undergoing aggregation, proliferation, and extensive neurite elaboration. The proliferation and differentiation of NEP cells induced by the interaction with laminin were dependent upon an early cell aggregation, since precoating of wells with poly-L-ornithine, a procedure which prevented such aggregation, completely blocked these responses. The previously reported proliferative effect of acidic fibroblast growth factor (FGF) on NEP cells was found to be synergistic with that of laminin. This observation is consistent with the idea that laminin may regulate cell responses in several ways: by direct stimulation via laminin receptors; by optimal presentation of FGF molecules to neural cells; and finally by upregulation of FGF receptor numbers on responsive cells. The in vitro response of laminin is mimicked by its long arm elastase digestion fragment, E8, whereas the cross arm fragment of laminin, E1-4, had no effect. In addition, antibodies specific for epitopes on the long arm blocked the effect seen with the whole laminin molecule. Binding studies of 125I-labeled laminin and its fragment performed on freshly isolated NEP cells confirmed the specificity of the in vitro observations: whole laminin and the E8 fragment bound to the NEP cell surface whereas the E1-4 fragment did not. These studies demonstrate mechanisms by which laminin, specifically through its long arm fragment, may assert a regulatory function during development of the mammalian central nervous system.