We performed a neurochemical study of the brain of two unrelated patients, living in different continents, with neuroacanthocytosis. The levels of monoamines and their metabolites, γ-aminobutyric acid and substance P, were measured in several brain areas and the monoamine metabolites in cerebrospinal fluid. The binding of 3H-spiperone to striatal membranes and to lymphoctytes was also measured. Both patients had a progressive neurological disorder with onset in the third decade of life and characterized by a complex movement disorder, epilepsy, muscular wasting, and changes in behavior. The movement disorder, epilepsy, muscular wasting, and changes in behavior. The movement disorder initially manifested with oromandibular dystonai and limb chorea, but at the time of death was characterized by a severe dystonic syndrome. The chemical changes were similar in the two patients. The most important neurochemical findings were a depletion of dopamine and its metabolites in most brain areas, most notably in the striatum, and elevation of norepiephrine levels in the putamen and globus pallidus. Substance P was markedly reduced in the striatum and substantia nigra. Our findings may provide clues to the neurochemical mechanisms underlying dystonia.