The migration of lymphocytes through monolayers of rat retinal pigment epithelium (RPE) and retinal vascular endothelium, which form the posterior and anterior blood-retinal barrier (BRB) respectively, was investigated in vitro. After a 4-hr assay the migration of untreated peripheral lymph node (PLN) cells through RPE monolayers was negligible (<1%) with only a small increase found after activation of the PLN cells with concanavalin A or by cross-linking CD3. Activation of the RPE with IFN-gamma augmented migration with maximal PLN cell migration being achieved with a combination of CD3 cross-linking and IFN-gamma activation (17% migration). The highest level of lymphocyte migration was observed with three CD4+ antigen-specific T cell lines specific for purified protein derivative (PPD; 33% migration), ovalbumin (OA; 31%), and S-antigen (S-Ag; 57%). Migration of both untreated and Con A-activated PLN cells through retinal endothelial cells (EC) from PVG rats was negligible, whereas the migration of the antigen-specific T cell lines was 23, 29 and 23% for PPD, OA, and S-Ag lines, respectively. Migration of these cell lines through retinal endothelium derived from Lewis rats was significantly greater (44% for PPD, 39% for OA, and 39% for S-Ag) which corresponded with a greater expression of ICAM-1 on the EC.