Prolonged gastrointestinal transit time is a prominent feature of many inflammatory bowel conditions, including severe ulcerative colitis,23 and cystic fibrosis.24,25 As gut motility involves the coordination of the nervous, gastrointestinal, and musculoskeletal systems,26 the mechanism behind the retarded movement in MPO−/− mice likely involves multiple factors. This evidence concerns the gene MPO and cystic fibrosis.