The transepithelial potential (TEP) and short circuit current (SCC) of the bovine retina pigment epithelium (RPE) were monitored throughout a 3hr period. Application of retinaderived factors to the apical side of the preparation resulted in a stabilization of the TEP and SCC, followed by a secondary rise in both electrical parameters. The late, secondary rise could be eliminated or reduced by the administration of cycloheximide suggesting a dependence upon protein synthesis. The active component(s) is not heat labile and has an apparent molecular weight between 1,000–10,000.After 3 hr of incubation, both control and factor-treated RPE had normal appearing nuclei and mitochondria; however, the factor-treated preparations were significantly thicker (apical to basal membrane) and had more apical processes than the control tissues.