Fusion of the microvilli of the enterocytes, breakdown of the microvillous structure, vacuolization of the cytoplasm, and separation of the cells from one another, were observed in the early period of anoxia in the isolated small intestinal loop of dog. Filling the intestinal lumen with isotonic glucose solution inhibited the occurrence of the morphological changes observed. These observations furnish new data to the understanding of the very initial stage of small intestinal cell destruction due to anoxia.