Background: Bipolar disorder (BD) has substantial morbidity and incompletely understood neurobiological underpinnings. Objective: To investigate brain chemistry in medication-free individuals with BD. Design: Two-dimensional proton echo-planar spectroscopic imaging (PEPSI) (32×32, 1-cm3 voxel matrix) acquired axially through the cingulate gyrus was used to quantify regional brain chemistry. Setting: The Center for Anxiety and Depression at the University of Washington in Seattle and the Bipolar Research Programs at McLean Hospital and the Massachusetts General Hospital in Boston. Participants: Thirty-two medication-free outpatients with a diagnosis of BD type I (BDI) or BD type II (BDII), predominantly in a depressed or mixed-mood state, were compared with 26 age- and sex-matched healthy controls. Main Outcome Measures: Tissue type (white and gray) and regional analyses were performed to evaluate distribution of lactate; glutamate, glutamine, and γ-aminobutyric acid (Glx); creatine and phosphocreatine (Cre); choline-containing compounds (Cho); N-acetyl aspartate; and myo-inositol. Chemical relationships for diagnosis and mood state were evaluated. Results: Patients with BD exhibited elevated gray matter lactate (P=.005) and Glx (P=.007) levels; other gray and white matter chemical measures were not significantly different between diagnostic groups. Isolated regional chemical alterations were found. An inverse correlation between 17-item Hamilton Depression Rating Scale scores and white matter Cre levels was observed for BD patients. Conclusions: Gray matter lactate and Glx elevations in medication-free BD patients suggest a shift in energy redox state from oxidative phosphorylation toward glycolysis. The possibility of mitochondrial alterations underlying these findings is discussed and may provide a theoretical framework for future targeted treatment interventions.