Experimental data indicate that mucosal CD4+ T cells play an important role in the pathogenesis of inflammatory bowel disease (IBD). Based on the pattern of cytokine production, CD4+ T cells may be distinguished into two different phenotypes. Th1 responses are characterized by secretion of interleukin (IL)-2, tumor necrosis factor (TNF)-α, lymphotoxin, and interferon (IFN)-γ and are associated with delayedtype hypersensitivity reactions, whereas Th2 responses, which are characterized by secretion of IL-4, IL-5, and IL-10, have been associated with humoral immune responses and allergy. To assess the number of IFN-α and IL-4 positive cells in IBD and normal intestinal specimens, frozen sections from intestinal specimens from 10 Crohn's disease (CD), 8 ulcerative colitis (UC), and 8 healthy controls were examined by immunohistochemistry. Monoclonal antibodies for CD3, CD8, IFN-γ, and IL-4 were used. T-lymphocyte infiltration and cytokine expression by epithelial, lamina propria, and submucosal cells were scored on a four-point scale by two independent observers who were blinded for the clinical data. One-way analysis of variance (ANOVA) testing was used for statistical analysis. In intestinal specimens from IBD patients, the number of CD3+ cells was found increased in the lamina propria and, within the submucosa, this increase was significant (p < 0.001). In CD the number of lamina propria IFN-γ positive cells was significantly increased as compared with controls (p < 0.002). In UC the number of both IFN-γ and IL-4 producing cells in the lamina propria was not significantly increased as compared with controls. The present results confirm the existence of a Thl-biased pattern production in CD but not in UC.