1. The intramural blood vessels of the human colon have been described. 2. Five methods that have been used to study colonic mucosal blood flow in patients with colostomies or with normal colons were briefly outlined along with some of the limitations of each technic. 3. It has been shown that the colonic mucosal blood flow in the human responds to heating or cooling an extremity, eating a meal, pharmacologic agents, and emotionally stressful situations. 4. Adequate evaluation of colonic mucosal blood flow requires the development of quantitative technics of measurement. It may be that methods of monitoring radioactive indicators with critically shielded detectors may meet some of these needs16 and offer a way of studying the intact colon of an unanesthetized human subject.