Irritable bowel syndrome (IBS), characterized by abdominal pain/discomfort and disturbed bowel frequency, is a common functional bowel disorder that accounts for a substantial proportion of patients seen in primary care and secondary referral centers. The impact on patients' quality of life and the economic burden on the community are considerable. However, the outcome of conventional Western medicine in treating IBS has been disappointing. Several potential new therapeutic agents have been withdrawn because of serious adverse events. Traditional Chinese medicine (TCM) has been used in the treatment of IBS for centuries in Asian countries but scientific evaluation of its therapeutic function is scarce. A methodologically strong trial of a 20-herb formula has shown significant benefit for IBS patients. However, the herbal formulation was inadequately characterized and defined for repeated clinical studies.