In the intestine large numbers of bacteria and their products are separated by a single epithelial layer from resident inflammatory cells (macrophages and lymphocytes). Many of these bacterial products, such as lipopolysaccharides and peptidoglycans, are potent stimulators of free radical and inflammatory cytokine production by macrophages. This can occur in vivo in response to mucosal invasion by enteropathogenic bacteria or because of inappropriate activation of these cells, as in chronic inflammatory bowel disease. In this review we present evidence for production of cytokines in normal intestine and in intestinal inflammatory conditions. The adverse effects of cytokine production upon intestinal homeostasis, in particular disruption of epithelial integrity and prothrombotic changes in the vascular endothelium, are also discussed.