It is generally accepted that a circulatory disorder of the bowel during the embryonic stage of development plays an important part in the occurrence of atresias of the small bowel and colon, with the exception of the septal types of atresia. In most cases, the cause of this disorder is not known. An experimental study, making use of chick embryos, is presented and the results are discussed. Two sets of experiments were conducted. In the first set the bowel of the chick embryo was subjected to temporary ischemia. In the second one the chick embryo was subjected to a period of general hypoxia. Temporary ischemia of the bowel frequently resulted in stenosis or atresia. The duration of the vascular occlusion was significant factor. Temporary general hypoxia resulted in serious morphologic changes of the bowel and the liver. Stenosis or atresia did not occur in this case, but there was a strong resemblance to the histopathological picture of neonatal necrotizing enterocolitis.