Scanning electron microscopy was used to study normal and ischemic dog ileum. Ileal ischemia was produced by complete ligation of a side branch mesenteric artery for two and four hours and by reduced blood supply by narrowing the artery (50%) for two and four hours. The tissue was fixed by immersion and processed for scanning electron microscopy. Tissue from the same sites was also prepared for light and transmission electron microscopy. Scanning electron microscopy showed the polygonal shaped epithelial cells covered by a regular array of microvilli. With transmission electron microscopy these microvilli appeared as closely packed, parallel, and cylindrical processes. During complete occlusion for two hours, the upper portions of the villi had severe damage where epithelial cells were missing. However, at the base of the villi, epithelial cells were recognizable with irregular shaped microvilli and the glycocalyx was fragmented. After four hours of ischemia, there was an absence of epithelial cells and blood vessels were greatly engorged, protruding against the basal lamina. By light microscopy villar architecture appeared unaltered with 50% reduced blood flow for two and four hours and the epithelial cells exhibited no unusual microvillar pattern. However, after 50% occlusion for four hours, the microvilli appeared wider by scanning electron microscopy. This was confirmed by transmission electron microscopy where the microvilli not only appeared wider but were also shortened. The glycocalyx was unaltered.