Recent studies demonstrate the majority of chronic fatigue syndrome and fibromyalgia patients suffer from bowel dysfunction, with the majority being irritable bowel syndrome (IBS). IBS can be significantly debilitating problem in its own right with chronic fatigue syndrome and fibromyalgia. It is a gastrointestinal disorder characterized by bloating, abdominal pain, diarrhea and/or constipation and the absence of any identifiable physical, laboratory or radiological abnormalities indicative of organic disease. The newest criteria (Rome II) for IBS include at least 12 weeks (need not be consecutive) in the preceding 12 months of abdominal discomfort that is accompanied by at least two of the following three symptoms: the abdominal discomfort or pain is (a) relieved with defection, (b) associated with a change in frequency of defecation and/or (c) associated with a change in the form or appearance of the stool. There are a number of medications that can decrease the symptoms of IBS, but there also are a number of factors that are associated with IBS and when these are identified and treated, the results can be significant. These include food allergies, gluten and wheat sensitivity and small intestine bacterial and yeast overgrowth (SIBO). A number of studies have documented a connection between SIBO and IBS. This especially appears to be the case with chronic fatigue syndrome and fibromyalgia patients, occurring in 70-90 percent of these patients. The small bowel should be free of bacteria and yeast, but when it is not, the food stuffs are utilized by these bacteria resulting in gas, inflammation, poor absorption, diarrhea and/or constipation. The dysfunctional immunity and frequent diminished stomach acid and digestive enzymes that is often present (including the use of medications designed to decrease stomach acid) in chronic fatigue syndrome and fibromyalgia make these patients more prone to SIBO and subsequently IBS. There are tests to determine if SIBO is present, including the hydrogen breath test. This involves giving the carbohydrate lactulose and measuring the amount of hydrogen expired by the breath. If certain carbohydrates, such as lactulose, are digested by intestinal bacteria instead of the small intestine or stomach, hydrogen gas is produced and can be measured from the expired breath. Samples are taken every 15 minutes for 2 hours. Due to the fact that SIBO is so common with CFIDS and fibromyalgia, that it can be safety eradicated and that significant improvement or elimination of IBS symptoms can be achieved with treatment, the time and expense of the test is not generally necessary. Eradication of the yeast and bacterial overgrowth can be instituted without undergoing the test, but in addition to eradicating the yeast and bacterial overgrowth, one must also address the other dysfunctions present in order to obtain long term improvement. If the predisposing factors are not addressed, the bacteria and yeast will again populate the small bowel and symptoms will return.