Pelvic magnetic resonance (MR) imaging is limited by lack of an effective bowel contrast agent. This study was performed to evaluate the efficacy of rectally administered barium sulfate as a contrast agent in pelvic MR imaging. Thirty-two patients were studied retrospectively to evaluate anatomic definition of the rectosigmoid colon. A commercially available barium sulfate suspension was administered rectally in 19 patients. Thirteen patients were imaged without barium. In the latter patients, anatomic definition of the rectum and sigmoid colon was poor to fair with all pulse sequences. Delineation of the rectum and sigmoid colon improved in patients who received rectal barium, owing to distention and marking of the bowel by the predominantly low-signal-intensity barium. Barium is a safe, inexpensive negative contrast agent for bowel that may improve pelvic MR imaging.