Gulf War illness (GWI), a chronic anddebilitating pain, headaches, impaired memory and thinking, fatigue, respiratory and gastrointestinalsymptoms, and skin abnormalities. Exposure and sensitivity to chemical, pharmaceutical and/orenvironmental toxins in a combat theater of operations is believed to be causative of the illness. Thepathobiological mechanisms of GWI are unknown; there are no validated diagnostic tests, nor are thereeffective treatments or cures. This is a case-control study consisting of 20 Gulf War veterans affectedwith GWI and 20 matched non-affected Gulf War veterans, who will serve as the normal control group. Allsubjects will undergo brain positron emission tomography and magnetic resonance imaging scans forassessments of metabolic or neurochemical disturbances that may be associated with GWI. In allconsenting participants, a lumbar puncture will be performed to obtain cerebrospinal fluid (CSF), whichwill be analyzed for abnormalities in biochemical compounds that may be related to GWI. The derivedneuroimaging and CSF metabolic or biochemical data will be compared between the groups to determine ifthere are abnormal changes in GWI veterans compared to controls, which may shed new light onto thepathophysiology of GWI, as well as serve as biomarkers of the disorder.