Lithium specifically and potentially inhibits membrane transport of choline. However, the effect of lithium on human neuronal choline content is unknown. This study was performed to determine if lithium alters the human brain choline concentration in vivo. In vivo proton magnetic resonance spectroscopy was used to compare the relative brain concentration of choline-containing compounds in seven lithium-treated patients and six lithium-free controls. No significant difference was observed in the mean relative choline resonance between the patient and control groups. Lithium treatment did not appear to alter the overall brain content of choline-containing compounds. It remains possible that a component of these compounds, particularly free choline, is elevated during lithium treatment.