Sixty cancer patients who were undergoing radiation therapy to the pelvis of at least 4,000 cGy in 20 fractions over four weeks were randomized to take or not take Metamucil. Results were analyzed for the presence of radiation-induced diarrhea in two groups: patients taking Metamucil (n = 30) or not taking Metamucil (n = 30). The Murphy Diarrhea Scale was developed to assist in the synthesis of data collected in daily patient-reported diaries. Results were analyzed using ANOVA F-tests. Metamucil significantly decreased the incidence (p = 0.049) and severity (p = 0.030) of diarrhea and showed a strong trend in reducing the use of anti-diarrhea medication (p = 0.062). According to this pilot study, Metamucil was an effective method of controlling radiation-induced diarrhea. Results of this pilot study have implications for clinical practice and nursing research.