The express purpose of this paper is to review and analyze and add to the literature six cases of carcinoid of the rectum and to discuss the role of serotonin in the diagnosis of carcinoid. By supplementing endoscopic examination with the more recent approach of determination of serotonin blood levels, the diagnostic armamentarium for detecting rectal carcinoid is vastly increased. A review of the literature reveals that 212 cases of carcinoid of the rectum have been reported up to the present date, and this number coupled with the 6 cases reported herein makes a total of 218 cases. Freund1 in January, 1957, mentioned 303 cases not reported in the literature which he had gleaned from a questionnaire type of survey from 1260 surgeons. In 1953 Buchanan2 reported a total of 77 cases of carcinoid of the rectum. The problem as to whether or not carcinoid of the rectum