After ligation of the vascular arcades of the upper jejunum in rats, the ischemic damage to the intestinal mucosa and its regenerative behavior after ischemia lasting 120 minutes were investigated with histological and enzyme-histochemical methods. During the ischemic injury of the jejunal mucosa, there is rejection of hydropically swollen epithelial cells into the intestinal lumen advancing from the tip to the base of the villi without a previously detectable loss of activity of the enzymes investigated. At the end of ischemia lasting 120 minutes, there is complete destruction of the villi as well as the upper portions of the crypts. After rapid re-epithelialization of the mucosal surface by a flat epithelium, reformation of villi begins already after a 24 h period of regeneration. On the third day of regeneration, the intestinal mucosa has plump villi again. Their epithelia already show the morphological characteristics of mature enterocytes. On the other hand, enzymatic maturation of the enterocytes is only concluded between the first and second week of regeneration. An altered proliferation kinetics of the crypt epithelia due to the repair process is discussed as cause of this delayed enzymatic maturation of the enterocytes relative to the morphological differentiation. Although the intestinal mucosa has a regular villous structure again after regeneration lasting 8 days, enzyme histochemical finding in the lamina propria indicate that the process of repair is only complete here in the sixth week of regeneration.