This project was designed to compare differences in brain proton spectra between children and adolescents with bipolar disorder (BPD) and gender and age-matched normal controls, and to measure changes in myo-inositol levels following lithium therapy, utilizing in vivo proton magnetic resonance spectroscopy (1H MRS). A single voxel (2x2x2 cm3) was placed in brain anterior cingulate cortex for acquisition of the 1H spectra at baseline and after acute (7 days) lithium administration in 11 children (mean age 11.4 years) diagnosed with BPD, and in 11 normal controls. Acute lithium treatment was associated with a significant reduction in the myo-inositol/creatine ratio. This decrement was also significant in lithium-responders when analyzed separate from non-responders. Compared to normal controls, BPD subjects showed a trend towards a higher myo-inositol/creatine during the manic phase. These preliminary data provide evidence that a significant reduction in anterior cingulate myo-inositol magnetic resonance may occur after lithium treatment, especially among responders. Follow-up studies involving a larger sample may allow us to confirm whether changes in myo-inositol associated with acute lithium therapy persist in long-term clinical response of patients with and without lithium compliance.