The motility of the descending colon was studied in nine patients before and after resection of the rectum for cancer. This operation parasympathectomises and generally also sympathectomises the remaining left colon. Motor activity was significantly reduced by sleep before and after surgery. There was also a reduction in awake motility after surgery which is attributed to extrinsic denervation. The reduced motility may explain the increased frequency of motions passed after surgery.