Epidermal growth factor (EGF) is mitogenic for bovine corneal endothelial cells in culture. Pretreatment with either retinoic acid or the synthetic analog CBS-211 A ((E)-4-[2-(2-isopropyl-5-thienyl)propenyl]benzoic acid) at 10-8-10-6M enhanced the EGF effect. This potentiating effect of retinoids contrasts with their intrinsic activity, which results in cell growth inhibition in the absence of growth factor. The present data emphasize the previously reported beneficial effect of retinoic acid on corneal endothelium wound healing. This effect could be related to the potentiation of endogenous growth factors and further underlines the importance of retinoids in the medical treatment of corneal endothelial lesions.