METHODS The objective of this study was to evaluate the histologic reconstitution of the small intestinal mucosa after a standardized ischemic injury and to determine if the early repair process takes place by cell renewal or migration of existing mucosal cells. Therefore, male Wistar rats, weighing 190 to 320 g, were subjected to total warm intestinal ischemia by means of a hydrostatic pressure clamp for 45 or 90 mins. These rats were compared to sham-operated controls. Intestinal biopsies were obtained just before reperfusion and at various times up to 48 hrs thereafter. Mucosal injury was evaluated microscopically by a blinded examiner. RESULTS Variable mucosal reconstitution occurred within 3 hrs, after 45 mins of ischemia, whereas mucosal repair required up to 18 hrs after 90 mins of ischemia. In a second series of experiments, 45 or 90 mins of ischemia and 5 hrs of reperfusion were followed by the iv administration of radioactively labeled thymidine. Intestinal biopsies were taken 1 hr later and prepared for autoradiography. No increase in mucosal mitoses was observed. CONCLUSIONS The mucosal reconstitution occurred rapidly after 45 mins and 90 mins of total warm intestinal ischemia and primarily through mucosal cell migration.