Antibodies to tumor necrosis factor (TNF)‐α have been recently proposed as effective treatment for patients with Crohn's disease. Here, we analyze the functional role of TNF‐α in a mouse model of chronic intestinal inflammation induced by the hapten reagent 2,4,6,‐trinitrobenzene sulfonic acid (TNBS) that mimics some characteristics of Crohn's disease in humans. Macrophage‐enriched lamina propria (LP) mononuclear cells from mice with TNBS‐induced colitis produced 10–30‐fold higher levels of TNF‐α mRNA and protein than cells from control mice. When mice with chronic colitis were treated by intraperitoneal injection of antibodies to TNF‐α, an improvement of both the clinical and histopathologic signs of disease was found. Isolated macrophage‐enriched LP cells from anti‐TNF‐α‐treated mice produced strikingly less pro‐inflammatory cytokines such as interleukin (IL)‐1 and IL‐6 in cell culture. The predominant role of TNF‐α in the mouse TNBS‐induced colitis model was further underlined by the finding that striking colonic inflammation and lethal pancolitis was induced in TNF‐α‐transgenic mice upon TNBS treatment. Conversely, no significant TNBS‐induced colitis could be induced in mice in which the TNF‐α gene had been inactivated by homologous recombination. Complementation of TNF‐α function in TNF^−/− mice by the expression of a mouse TNF‐α transgene was sufficient to reverse this effect. Taken together, the data provide direct evidence for a predominant role of TNF‐α in a mouse model of chronic intestinal inflammation and encourage further clinical trials with antibodies to TNF‐α for the treatment of patients with Crohn's disease.