Abstract: Virtual colonoscopy is a non-invasive computerized medical procedure for examining the entire colon to detect polyps. We present an interactive virtual colonoscopy method, which uses a physically-based camera control model and a hardware-assisted visibility algorithm. By employing a potential field and rigid body dynamics, our camera control supplies a convenient and intuitive mechanism for examining the colonic surface while avoiding collisions. Our Z-buffer-assisted visibility algorithm culls invisible regions based on their visibility through a chain of portals, thus providing interactive rendering speed. We demonstrate our method with experimental results on a plastic pipe phantom, the Visible Human, and several patients.