Dendritic cells are antigen presenting cells that are likely to be pivotal in the balance between tolerance and active immunity to commensal microorganisms that is fundamental to inflammatory conditions, including Crohn's disease and ulcerative colitis. Interactions between dendritic cells and microbial products are discussed and how they contribute to regulation of immune responses. The concept that interactions between dendritic cells and commensal organisms may be responsible for maintaining intestinal immune homeostasis is also explored.