Specific in vivo T cell activation initiated by treatment with anti-CD3 antibodies leads to diarrhea and structural damage of the intestinal mucosa. In this study, the effect of T cell-induced mucosal damage on jejunal epithelial ion transport, muscle contractility, and neuronal ACh release was assessed in Ussing chambers, organ baths, and a specialized perfusion apparatus, respectively. Time-matched control mice received hamster serum containing irrelevant antibodies. Jejunal segments from anti-CD3-treated mice displayed a significantly elevated epithelial baseline short-circuit current (which indicates increased ion transport) and a concomitant reduction in responsiveness to prosecretory stimuli (nerve stimulation, carbachol, and forskolin). Longitudinal smooth muscle displayed altered spontaneous contractile activity, length-tension relationships, and carbachol-stimulated contraction in tissues excised from mice 20 and 40 h posttreatment. Anti-CD3 treatment did not affect stimulated ACh release from myenteric plexus neurons. We conclude that specific T cell activation via anti-CD3 antibody results in dramatic alterations in jejunal epithelial and smooth muscle function. Such T cell-induced changes in intestinal function may contribute to the symptomatology of T cell-mediated enteropathies, including graft-versus-host disease, celiac disease, and idiopathic inflammatory bowel disease.