Long-term cultures of bovine retinal capillary endothelial cells (BRCEC) have been established using bovine retinal pericyte conditioned medium (PCM). PCM had greater mitogenic activity on BRCEC than unconditioned medium (P less than 0.01). The mitogenic activity of PCM was not cell specific since bovine Tenon's fibroblast conditioned medium also had significant activity. PCM's activity was not enhanced by heparin though it was additive to that of retinal crude extract.