PURPOSE: Radiation has become an adjunct in the treatment of pelvic malignancies. Attempts to prevent adjacent tissue injury have met with varying degrees of success, and the purpose of this study was to investigate potential radioprotective effects of an elemental diet, sodium meclofenamate, and vitamin A in an animal model of acute and chronic pelvic radiation previously described. METHODS: Female Sprague-Dawley rats, 200-250 grams, were anesthetized and then received 900 rads of pelvic radiation once per week for five weeks for a total of 4500 rads. Animals were divided into five groups. Treatment groups received radiation and elemental diet, radiation and vitamin A, radiation and sodium meclofenamate. Control animals received anesthesia only and no radiation. Vitamin A was given as a supplement to (662 IU/kg) standard rat chow. Elemental diet was given as a commercially available formula, whereas sodium meclofenamate was given as a postoperative supplement (5 mg/kg/day). All animals were given these treatments during the course of radiation therapy only. Histology of distal colon was measured at one week, five weeks, six months, and one year postradiation therapy. The distal two cm of colon were removed at necropsy and fixed in 10 percent formalin at each of the above time points. Histologic grade was determined by a previously described grading scale. RESULTS: Results showed a qualitative radiation injury that could be documented at one and five weeks postradiation. Elemental diet, vitamin A, and sodium meclofenamate prevented histologic changes that occurred at these time points. No difference in histologic grade was seen between any groups at six months and one year postradiation therapy. CONCLUSION: In summary, our model of pelvic radiation produces a definable radiation injury within the colon at one and five weeks postradiation. Use of elemental diet, vitamin A, and sodium meclofenamate prevented these changes. © 1994 American Society of Colon and Rectal Surgeons.