There are currently a number of major drawbacks to using a colonoscope that limit its efficacy. One solution to this may be to use a warm liquid to distend the colon during inspection. Another is to replace the colonoscope with a small mobile robot-a solution many believe is the future of gastrointestinal intervention. This paper presents RollerBall, an intraluminal robot that uses wheeled-locomotion to traverse the length of a fluid-filled colon. The device provides a central, stable platform within the lumen for the use of diagnostic and therapeutic tools. The concept is described in detail and the feasibility demonstrated in a series of tests in a synthetic colon.