Tissue transition projection (TTP) represents a three-dimensional reconstruction technique for volumetric image data sets. To demonstrate the principle characteristics of TTP, a simple phantom consisting of two pipes with a simulated, wall-adherent polyp was scanned with spiral CT, and images were reconstructed by means of volume rendering for both opaque surface reconstructions and TTP. Tissue transition projection was used in 7 patients for reconstruction of the small intestine or the colon. Unlike three-dimensional reconstructions with opaque surfaces, TTP enhances surface transitions while suppressing homogeneous areas, allowing delineation of the bowel wall similar to conventional double-contrast studies.