The adverse impact of Gulf War Syndrome (GWS) on the health of veterans and on the resources of the VA Healthcare System underscores the need to resolve its underlying cause. In response, the investigators propose to investigate the central hypothesis that gut bacteria may be responsible for symptoms associated with GWS. The investigators will enroll a total of 120 patients with GWS and 90 healthy controls.

The investigator will assess the prevalence and role of abnormal gut microbial fermentation among Veterans with GWS and investigate the efficacy of diagnostic and treatment strategies directed at indigenous gut microbes in the management of GWS.

Inclusion Criteria:

• Gulf War Veterans meeting the 1994 Centers for Disease Control and Prevention (CDC) criteria for the diagnosis of Chronic Fatigue Syndrome(CFS), i.e > six months of one or more symptoms from at least two of the following three clusters: general fatigue, mood and cognitive abnormalities, and musculoskeletal pain
• Must be under the care of a primary physician and have had a previous diagnosis of Gulf War-related illness or GWS and have medical records documenting investigations to rule out other causes of fatigue
• Minimum of the following laboratory screening tests: complete blood count with leukocyte differential, erythrocyte sedimentation rate, serum electrolytes, calcium, glucose, blood urea nitrogen, creatinine,urinalysis, and thyroid function tests
• Subjects must also have a GI consult first as part of routine care to confirm eligibility and availability
• Patients with Irritable Bowel Syndrome (IBS), fibromyalgia (FM), anxiety or depression will not be excluded, but will be identified for subgroup analysis
• Healthy controls will be screened with complete blood count (CBC) and comprehensive metabolic panel to confirm eligibility

Exclusion Criteria:

• History of peptic ulcer, inflammatory bowel disease, diabetes, cirrhosis, rheumatoid arthritis, lupus, narcotic dependence,celiac disease, tropical sprue, bowel resection(including gastric, small bowel or colon; but gallbladder surgery or appendectomy are NOT exclusion criteria)
• Patients with chronic illness (HIV, tuberculosis)
• Pregnant or breast-feeding, psychotic depression, bipolar disorder, schizophrenia, eating disorders
• Healthy subjects will be excluded if their questionnaire indicated abnormal symptom profile