The retinal pigment epithelium (RPE) and associated Bruch's membrane are a very complex tissue, which in vivo responds to environmental changes and pathologic stimuli in a diverse manner. Proper function of the RPE is essential to normal vision. One principal function of RPE is the phagocytosis of rods and cones and as a light absoring tissue to begin the complex chain of chemical reactions which transform the light impluse into an electrical impulse. Under pathological conditions the RPF cells can undergo changes, e.g., hyperplasia, metaplasia or degeneration (senile macular degeneration) associated with total or partial loss of vision. Likewise, Bruch's membrane can undergo changes (angoid streaks, drusen) which results in impaired vision. Unfortunately, the many diseases involving the RPE-Bruch's membrane complex usually progress relentlessly. The ophthalmologist is helples in attempts to alter the course of the diseases because of the lack of knowledge of the cell biology of RPE. Our proposal is aimed at elucidating the mechanism controlling the life-cycle of the RPE and its contribution to the synthesis and maintenance of Bruch's membrane. We have established a culture system of porcine RPE which morphologically maintain their differentiated state. This model system will allow us to investigate the effect of several factors on some growth parameters of RPE as well as the conditions which favor RPE survival and ability to synthesize an extracellular matrix whose components are similar to Bruch's membrane.