To clarify the changes in vascular resistance in Crohn's disease, we studied changes in the thickness of arterial media histometrically. The resected specimens of mesenterium and intestine from 18 patients with Crohn's disease were used. Each intestinal lesion was classified into three grades: no inflammation, exudative change, and fibrosing change. In the ileum, significant atrophy in the media of the submucosal peripheral arteries was noted during exudative and fibrosing changes, while in the submucosal larger vessels or in the mesenterium, the thickness of the arterial media did not change. In the colon, atrophy in the media of the submucosal arteries was noted in all stages except in the larger vessel during exudative change, while no significant changes were noted in the mesenterium. In conclusion, it is suggested that circulatory disturbance occurs even in the early stage in Crohn's disease, and there seems to be increased vascular resistance in the area between the deep submucosal and the distal mesenteric arteries.