Alterations in colonic motility appear to exacerbate the symptom of increased frequency of bowel movements in patients with ulcerative colitis. Decreased segmenting contractions allow rapid forward movement of luminal contents accentuating the diarrhea. The decrease in segmenting colonic motility is further exacerbated by increased numbers of propagating contractions. The rapid transport of intraluminal contents with a propagating contractions into a nondistensible rectum may be one explanation for the relative high incidence of fecal incontinence in these patients. The pathogenesis of the decreased segmenting contractions appears due to an electromechanical dissociation resulting from inhibition of myosin light chain phosphorylation. It is possible that several inflammatory mediators including free oxygen radicals decrease smooth muscle cell function.