Article abstract—We performed a short-term, double-blind, placebo-controlled, crossover trial of sodium dichloroacetate (DCA) therapy in 11 patients affected by various primary mitochondrial disorders. Independent measures of ox-idative metabolism (venous blood metabolites, exercise testing, phosphorus magnetic resonance [MR] spectroscopy of muscle, and proton MR spectroscopy of brain) were used in order to monitor metabolic responses to the drug. One week of DCA treatment produced significant decreases (p < 0.05) in blood lactate, pyruvate, and alanine at rest and after bicycle exercise. Proton MR spectra collected from a supraventricular volume of interest in brain of seven of ll patients also showed significant changes. Brain lactatekreatine ratio decreased by 42% during DCA treatment (p < 0.05). Brain cholinelcreatine ratio (which is low in patients with myelinopathies) increased by 18% (p < 0.01) after therapy. N-Acetylaspartatelcreatine ratio (an index of neuronal damage or loss) increased by 8% after treatment (p < 0.05). Proton MR spectra collected in two of 11 patients from a volume of interest including the basal ganglia showed similar results (decrease of 36.6% in lactatekreatine; increases of 16% in cholinelcreatine and 4.5% in N-acetylaspartatelcreatine). Phosphorus MR spectroscopy of muscle and self-assessed clinical disability were unchanged. Our study indicates that short-term DCA treatment not only lowers blood lactate but also improves indices of both brain oxidative metabolism and neuronal and glial density or function.