In a double-blind randomized placebo-controlled study, including 70 patients treated with radiotherapy of localized malignancies in the pelvis, the effects of prophylactic sucralfate in preventing bowel discomfort were evaluated. Radiotherapy was delivered in a conventional manner with high-energy photons in a total dose of 62-66 Gy (target dose, 1.8-2.2 Gy) during 6.5 weeks. Dose granules of sucralfate or placebo were given 2 weeks after irradiation started and continued for 6 weeks. All analyses were performed blindly. The patients in the sucralfate group had significantly less problems with acute (5 weeks) and chronic (66 weeks) bowel discomfort. The consumption of loperamide was also reduced in the sucralfate group, and the weight decrease was less pronounced. No adverse effects were seen. Thus, sucralfate seems to be beneficial in minimizing the problems of bowel discomfort during and after irradiation of malignancies in the pelvis. These results are discussed in relation to other related observations.