||Brain growth in chick embryos is regulated by both mechanical and chemical factors. The translation of mechanical stress into chemical signals in the expanding brain is the thrust of this study. Occlusion of the neural tube at a time point prior to the time of natural occlusion precociously induces rapid brain expansion in the chick embryo. Conversely, releasing the pressure of the closed system that induces rapid brain growth causes a decrease in neuroepithelial cell proliferation. Thus, pressure is a key factor in normal brain growth. FAK is a membrane-associated protein that can send mitogenic signals to nuclei. It can be activated by trans-membrane integrins which change conformation in response to pressure from outside the cell. FAK activity is increased in response to increased pressure in several different tissue types. FAK can activate Src and ERK as subsequent downstream proteins which are involved in mitogenic signaling. This study aims to show the presence of FAK, Src, and ERK in both their total and phosphorylated forms in embryonic chick neuroepithelium and to analyze the activity of these proteins on a temporal basis.