BACKGROUND: Epidermal growth factor (EGF) and transforming growth factor-␣ (TGF␣) regulate cell proliferation and differentiation in the embryo. The induction of cleft palate (CP) by all trans-retinoic acid (RA) was associated with altered expression of TGF␣, EGF receptor, and binding of EGF. This study uses knockout (KO) mice to examine the roles of EGF and TGF␣ in teratogenic responses of embryos exposed to RA. METHODS: Pregnant wild-type (WT) mice of mixed genetic background, EGF KO, C57BL/6J, and TGF␣ KO mice were given a single oral dose of RA (100 mg/kg, 10 ml/kg) or corn oil on GD 10 at 12 pm, GD 11 at 12 pm or 4 pm, or GD 12 at 8 am or 12 pm (plug day ϭ GD 0). GD 18 fetuses were examined for external, visceral, and skeletal effects. RESULTS: After exposure to RA on GD 12, the incidence of CP in EGF KO was significantly reduced relative to WT. In TGF␣ KO fetuses, RA exposure on GD 10 increased the incidence of CP versus C57BL/6J. The incidence of skeletal defects in the limbs, vertebrae, sternebrae, and ribs were also affected by lack of expression of EGF or TGF␣ with region-specific amelioration or exacerbation of the effects of RA. In TGF␣ KO fetuses, incidences of forelimb long bone and digit defects increased relative to C57BL/6J. In EGF KO fetuses, relative to WT, the incidence of hindlimb oligodactyly was increased. In EGF KO, but not WT, RA produced short, bent radius, humerus, and ulna. Both TGF␣ and EGF KO mice had increased incidences of dilation of the renal pelvis and this was reduced by RA. CONCLU-SIONS: RA exposure produced skeletal and visceral defects in all genotypes; however, EGF or TGF␣ KO influenced the incidence and severity of defects. This study supports a role for EGF and TGF␣ in the response to RA. Birth