||The chick embryonic brain undergoes rapid expansion dependent upon the buildup of pressure after occlusion of the spinal neurocoel. Initially, the brain consists of more cavity than tissue and expands from the accumulation of cerebrospinal fluid (CSF). Fluid accumulates by the continual transport of fluid across the neuroepithelium via an osmotic gradient while the brain cavity is a closed system. However, it is likely that both chemical factors within CSF and intra-luminal pressure (ILP) promote morphogenesis, histiogenesis, and embryonic brain growth by their cooperative interactions. The purpose of this research is to verify FGF2 within the chick embryonic CSF and neuroepithelium and that the receptor for FGF2 is within the neuroepithelium; to demonstrate that when FGF2 is blocked with specific antibodies in both the CSF and neuroepithelium, the brain will still expand due to an increase in intraluminal pressure; to verify the antibodies to FGF2 do in fact block functionally. This study indicates that intra-luminal pressure is likely responsible for the early embryonic brain expansion.