Recently, the use of tegaserod and alosetron -- drugs approved for the treatment of irritable bowel syndrome (IBS) -- has been restricted because of adverse events. This has resulted in a need for additional modalities for the treatment of IBS. Our objective was to determine the effectiveness of probiotics in the global relief of symptoms associated with IBS and in the improvement of flatulence, abdominal pain, transit time, and bacterial counts. Using the MEDLINE database from 1966-October 2007 and manually searching article references for relevant articles and abstracts, we identified 14 blinded, placebo-controlled clinical trials of the effectiveness of probiotics in the treatment of IBS. Of 11 studies in which overall symptom relief was assessed, seven indicated a significant improvement with probiotics versus placebo. Five of eight investigations of abdominal pain and distention revealed a benefit with probiotic use. Four studies demonstrated an improvement in symptomatic flatulence in probiotic treatment groups, whereas one study showed no significant benefit. Four of five studies of the effects of probiotics on colonic transit time revealed a benefit compared with placebo. As probiotics have shown benefit and possess a favorable adverse-effect profile, their use may represent an option for symptom relief in patients with IBS. However, additional data are necessary before probiotics can become a standard of care in the treatment of IBS, a complex and chronic condition.