The mucosal surface pattern of surgical specimens from small intestine affected by Crohn's disease are studied using Alcian-green staining of whole mounts. The semimacroscopic appearance of the mucosa is described. Our findings include i.a. malformation and enlargement of villi-often to extreme degree-villi frequently showing small vesicles on their apical region. Polypoid structures were found to be avillous as well as covered by normal or abnormal villi. The semimacroscopic observations are compared with observations from conventional light microscopy. The villus enlargement is in the first stages caused by lymphatic dilatation and later by oedema and inflammation.