The interest for retinoic acid (RA) has been increased the last few years, because of its central role in the coordination of development and homeostasis. The present study aims to explore the differential effect of different concentrations of RA during morphogenesis of the chick embryo. Fertilized eggs of Gallus domesticus were injected with a single dose of 0.5 µg, 1 µg or 2 µg of RA dissolved in 1 µl of dimethylsulphoxid (DMSO). Injections were carried out after three days of incubation. RA treatment induced teratogenic effect during the morphogenesis of the developing chick embryos. The defects included malformations in the brain, head, eyes, nostrils, beak, trunk region, fore- and hind-limbs and tail region. The explanation of the RA effect based on the disturbance of normal pattern of expression of genes concerned with the process od morphogenesis. Where the excess of the exogenous RA caused overexpression of genes resulted in several malformations in the developing embryo. The higher concentrations of RA in the present work induced the production of large amounts of the catabolic enzymes (cyps) that degraded RA and minimized the teratogenic effect of RA to a level lower than that induced by lower concentration of RA. The differential effect of different concentrations of RA was controlled by the degrading enzymes through a feedback controlling system.