Co-culture of rat retinal pigment epithelial (RPE) cells or retinal capillary endothelial (EC) cells with T lymphocytes from immunised syngeneic rats indicated that RPE cells but not EC could process retinal S-antigen and induce antigen specific T cell activation. Activation of lymphocytes by EC however was also antigen independent, and may be due to T cell (CD2) endothelial cell (LFA-3) ligand interactions which are functional on EC but not RPE.