Mice infected with Trichinella spiralis developed significant enteropathy, comprising villus atrophy, crypt hyperplasia, goblet cell hyperplasia and a decrease in intra-epithelial lymphocyte numbers by 10 days post-infection, when most of the parasites had been expelled from the gut. However, worm expulsion was prevented by treatment with cyclosporin A and, despite a continued parasite burden, cyclosporin A treated animals had no villus atrophy or changes in inflammatory cell numbers. These results confirm that the expulsion of T. spiralis from the mouse gut is accompanied by a significant intestinal lesion and that both of these phenomena are T-cell mediated.