The effect of retinoic acid on DNA synthesis and cell morphology was studied using corneal stromal fibroblasts in culture. All-trans retinoic acid induces an increase in DNA synthesis after 24 hours of exposure. Autoradiographic studies of3H-thymidine incorporation into corneal stromal cells exposed to 10−6M retinoic acid for 24 hours showed an increase in labeling which ranged from 19.2% to 67.6% over control cultures. Scintillation analysis of labeled cultures also showed an increase in incorporation of3H-thymidine into cells treated with 10−6M retinoic acid, with increases ranging from 21.8% to 114.7% above control cultures. Exposure of cultured corneal stromal cells to 10−6M retinoic acid resulted in a dramatic change in cell morphology such that they changed from spindle-shaped to round, flattened cells which were epithelioid in appearance. These data demonstrate the biological activity of retinoic acid in stromal fibroblasts and imply a role for vitamin A in maintenance of stroma structure and function.