The success of biological therapy is best advocated by infliximab (IFX), which has dramatically improved medical therapy for Crohn's disease and now has been shown to be effective in the treatment of ulcerative colitis. Other anti-tumor necrosis factor (TNF) compounds have been tested in the treatment of Crohn's disease and will soon appear in the therapeutic armament. However, neutralization of TNF does not seem to be the most important mechanism of action of these therapies. Apoptosis of activated T cells was demonstrated after IFX treatment, and this may be the key to its success. Thus, other therapies that induce apoptosis in activated T cells, such as visilizumab, have a great chance to be of benefit. Biological therapies applied in inflammatory bowel disease appear to be safe, although therapy-related adverse events clearly have been recognized.