In 60 cases of rectal cancer who underwent sphincter-preserving operations between 1962 and 1975, post-operative ano-rectal functions were examined by means of subjective symptoms, digital examination through the anal canal, the pressure inside the anal canal, electromyography of the external sphincter, anal canal sensory examinations, reflex of the internal sphincter and radiography of the rectum. In 28 cases of anterior resection, the post-operative ano-rectal functions were good as long as there was no stenosis in the junction part. In patients who underwent the invagination type operation, the ano-rectal functions were also good as in the anterior resection cases. In cases of the pull-through operation, the ano-rectal functions in the initial post-operative period were worse than those for the other types of operation. The reason for this is thought to be the loss of the internal sphincter reflex and the decrease in reservoir continence due to defective ampulla formation. However, two years after the operations, the ano-rectal functions of these patients showed considerable improvement. In particulart, ano-rectal functions were good when the post-operative ampulla formation was good even when there was no internal sphincter reflex but the functions were disturbed in some way if there was internal sphincter reflex but poor ampulla formation. From animal experiments, it was evident that rectal ampulla is an important factor in post-operative ano-rectal functions.