Cancer treatment regimens that include radiation therapy (RT) to the abdominal region for cervical, ovarian, prostate, sigmoid, or colorectal cancer potentially disturb the colonization resistance of the indigenous gut flora, causing RT-induced diarrhea, enteritis, and colitis in more than 80% of patients with cancer. One approach for the prevention of RT-induced diarrhea is the use of probiotics. Randomized clinical trials have demonstrated efficacy of probiotic preparations VSL #3 and Lactobacillus casei DN-114 001 in decreasing the incidence and grade of RT-induced diarrhea. Oncology nurses and advanced practice clinicians are in a position to interpret research findings related to RT-induced diarrhea, enteritis, and colitis and to apply evidence-based practice principles in patients with cancer receiving RT to promote positive outcomes.