A number of parameters of ano-rectal function were measured in 10 patients with adult megacolon and the values compared to those in an age- and sex-matched group of normal volunteers. The absence of inhibition of force in the anal canal on rectal distention in patients with adult Hirschsprung's disease was the most constant finding although a group of patients were shown to have high resting and canal pressures resulting in megacolon. No constant sensory or myoelectrical abnormality was apparent within the anal canal. However, an unusual electrical rhythm was noted from the rectum in 1 patient with adult Hirschsprung's disease.