The purpose of these studies is to determine the colonic myoelectrical and contractile response after eating a 1000 calorie meal in patients with active ulcerative colitis. During fasting, slow waves are identifiable significantly more in patients with ulcerative colitis than in normal subjects (p < 0 . 01). The predominant slow wave frequency is 6 . 1 +/- 0 . 2 cycles/min, which is similar to the normal subjects. The slow waves are not altered by eating in either group. Minimal spike or contractile activity occurs during the fasting period both in patients with ulcerative colitis and in normal subjects. In patients with ulcerative colitis, spike activity increases rapidly after eating the 1000 calorie meal (P < 0 . 01), but the maximal response is decreased and shorter in duration than in normal subjects. There is no simultaneous increase in colonic contractility above fasting levels after the meal in patients with ulcerative colitis. This is strikingly different from the simultaneous increase in contractile and spike activity (P < 0 . 01) that occurs after eating in normal subjects. These studies suggest that in ulcerative colitis (1) the colonic smooth muscle slow wave activity is intact; and (2) a disturbance in the normal colonic contractile response to eating is present despite an adequate spike response. This lack of colonic contractility may contribute to the increase in diarrhoea that occurs in these patients after eating.