AbstractConcanavalin A (con A) is teratogenic to rabbit embryos during gestational days 12–15. Intracoelomic injections of 40 μl con A solution (4 μg/μl) were performed on rabbit embryos during gestational days 10–15. Control embryos received either 40 μl of saline, sham injection or no treatment. Con A caused increased fetal resorptions on days 10 and 11, but malformation levels did not differ from controls. On days 12–15, con A produced craniofacial, trunk and limb anomalies. The highest percentage of malformations occurred on day 14. The defects were classified into four groups: (1) malformations of limbs including paw and digital dysplasias as well as fusions of the limbs to the head or body wall; (2) “closure” defects such as umbilical hernia, encephalocoele, exencephaly or ectopia cordis; (3) “contracture” defects such as club paws, extended knees, or clenched digits, which exhibited normal osseous and cartilaginous skeletons; and (4) miscellaneous, non‐specific anomalies including fused or dysplastic sternebrae or ribs. Histologic analysis of selected 12‐day embryos 4 to 18 hours post‐injection was performed to ascertain potential sites of teratogenic action. At 12 hours ectodermal necrosis was observed in the limb buds adjacent to the apical ectodermal ridge. By 18 hours, the ectoderm had eroded, exposing the basal lamina to the amniotic fluid. Focal areas of mesenchymal necrosis were observed in association with the ectodermal erosion. The potential roles of amniocentesis and limb bud repair in the genesis of the malf