Dissociated cells from chick embryo encephalon of 36 h of incubation have been cultivated on fibroblast, meningeal cell, or glial layers. Within the first 24 h of cultivation, cells adhered to the preformed layers more firmly than to plastic or collagen surfaces. After 48 h of cultivation, the brain cells cultured on meningeal cell or fibroblast layers behaved very similarly to those cells cultured on plastic surfaces. But when cultured on glial layers for 3 days, the brain cells differentiated into characteristic neuroblasts, as demonstrated by specific neuronal stainings. These results support the hypothesis of a stimulatory role of glial cells in neuronal differentiation. The possible causes of this stimulatory action are discussed.