Inflammatory bowel diseases (IBD: Crohn's disease, ulcerative colitis) are chronic inflammatory and frequently relapsing diseases of the gut that ultimately lead to destruction of the intestinal tissue. Recent evidence suggests that a pathologic activation of the mucosal immune system in response to antigens is a key factor in the pathogenesis of IBD. Furthermore, changes in cell migration and cytokine production appear to contribute to the perpetuation of IBD and the postoperative recurrence of Crohn's disease. Based on recent advances in our understanding of the pathogenesis of IBD, several new therapeutic strategies are currently being tested in clinical practice, including recombinant anti-inflammatory cytokines (IFN-alpha, IL-10, IL-11) and inhibitors of cell adhesion molecules (ICAM), proinflammatory cytokines (TNF, IL-12) and their receptors (TNF, IL-6R).