Small intestinal mucosal lesions, characteristically restricted to the villous tissue, have been described in shock states of different types. We have found this type of mucosal lesion in a standardized intestinal ischemia shock in rat. The pathophysiology of the mucosal lesion has been debated. In earlier work we noted a tenfold increase of platelets in the ischemic intestine. The importance of reperfusion and local platelet accumulation for the development of ischemic lesions in the intestinal mucosa was studied. Biopsy specimens taken immediately before and after reperfusion of the ischemic small intestine showed the same degree of mucosal lesion, i.e. total disintegration of the lamina propria. In thrombocytopenic rats subjected to intestinal ischemia, the severity of mucosal lesion was the same as in normothrombocytic rats. The results indirectly support the hypothesis of local villous oxygen deficit as the pathophysiologic mechanism leading to lesions of the small intestinal mucosa in shock.