The intestinal mucosa has to discriminate between beneficial and pathogenic organisms within the gut, a process regulated in part by specific T cells that secrete immunosuppressive cytokines. Interleukin-10 (IL-10) mediates immunoregulatory mechanisms that control inflammatory responses in the gut, and evidence is accumulating that it may have a role in the pathology of Crohn disease and ulcerative colitis, conditions collectively encompassed by the term "inflammatory bowel disease." Long-term administration of IL-10 to treat the disease is problematic because no effective delivery method has been available. In the June 16 Nature Biotechnology, Lothar Steidler and colleagues at Ghent University report a recombinant bacteria developed to produce IL-10 that also addresses the issue of containment of a live genetically modified organism following its release into the gut environment for therapeutic use (Nature Biotechnology, DOI:10.1038/nbt840, June 15, 2003).