Primary retina-derived endothelial cells isolated from bovine and other animal tissues are extremely useful for studying the molecular mechanisms involved in the pathogenesis of diabetic retinopathy. Preparations of primary bovine retinal endothelial cells (BREC), however, usually contain a number of contaminating non-endothelial cells, e.g. pericytes which have been shown to inhibit proliferation of endothelial cells. To overcome this major drawback, we immortalized BREC by reconstitution of telomerase activity as a consequence of CMV promoter-driven expression of the catalytic domain of human telomerase. Immortal BREC (iBREC) have the capacity to proliferate for >90 passages over 10 months and constantly express endothelial marker proteins. In addition, iBREC behave like BREC with respect to stimulation of proliferation with VEGF, IGF-1 and bFGF, indicating that we have generated a stable endothelial cell line closely related to the corresponding primary cells.