The basal motility of the sigmoid colon and rectum was evaluated manometrically over 3 consecutive 10-minute periods in 29 control subjects, 14 chagasic patients without megacolon, and 32 chagasic patients with megacolon. The results indicated that the sigmoid colon of both chagasic groups had a lower motility index and lower wave frequency than that of the controls. Reduced wave frequency was observed in the rectum of patients with megacolon, out the rectum of the chagasic patients without megacolon showed manometric characteristics similar to those for the controls. The abnormalities observed were attributed to intramural denervation of the viscera under study. Waves of long duration were observed very frequently in megacolon, and were assumed to be caused by dilatation in itself and not by abnormal contraction of muscle fibers.