Intestinal muscle and the autonomic nervous system constitute a neuromuscular unit. A clinical study was undertaken to seek neurogenic causes of impaired motility affecting the rectosigmoid junction and rectum. Patients with primary chronic constipation were shown by enzyme-histochemical examination of biopsies to have neuronal colonic dysplasia of the rectosigmoid, whereas the latter was normally innervated in healthy controls. The present investigations provide a fresh insight, underpinned by histological findings, into the aetiology of chronic constipation and make a contribution to its operative treatment.