For the purpose of making clear the nervous mechanism in the aganglionic bowel segment of Hirschsprung's disease, electrophysiological and pharmacological studies were carried out on the muscle strips of the aganglionic and normal bowel segments of mouse and human. The aganglionic and normal bowel of mouse were obtained from piebald mouse and its normal sibling. Both the aeanglionic and normal bowel of human were obtained from the patients of Hirschsprung's disease at the corrective surgery. The junction potentials and tension developments in muscle evoked by field stimulation were recorded and analyzed by autonomic blockers. For recording the membrane potential and tension in muscle, the double sucrose gap method was used. In the normal segment, both excitatory and inhibitoay junction potential (e.j.p. and i.j.p.) evoked by field stimulation were recorded. After application of atropine or tetrodoxin, e.j.p.s disappeared. I.j.p.s were resistant to phentolamine and propranolol, but disappeared after application of tetrodotoxin. However, in the aganglionic segment, neither junction potentials nor tention developments were recorded at all. It was concluded from the present study that the aganglionic bowel segment is in a denervated condition without any nervous control.