The present investigation was designed to study the effect of anger on colon motor and myoelectric activity in irritable bowel syndrome. Patients with irritable bowel syndrome were compared with normal controls during resting and two anger stressors: criticism of performance on an intelligence test and during a delay of assistance for a diagnostic procedure. At rest patients with irritable bowel syndrome had higher motor and spike potential activity than normal subjects; however, the difference was only significant for spike activity. Anger significantly increased colon motor and spike potential activity in the groups compared with the resting state. Patients with irritable bowel syndrome produced significantly higher motor and spike potential activity when angered. They also reported themselves to be more hostile and appeared angrier than normal controls after the study. However, they did not report themselves to be more anxious or depressed, suggesting that the observed changes in colonic function of both groups were due to anger. Patients with irritable bowel syndrome scored significantly higher than controls on the Minnesota Multiphasic Personality Inventory scales of hypochondriasis, hysteria, and depression, but these personality factors did not significantly influence their anger level before the study. The results are discussed in terms of the role of learning in the colon and the abnormal reinforcement of bowel behavior in patients with irritable bowel syndrome.