Lithium (Li) and its salts have been demonstrated to be the most effective drug in both acute and prophylactic treatment of bipolar disorder. The exact molecular mechanisms and particular target regions accounting for its mood-stabilizing effect remain unknown. Knowledge of Li distribution and its regional pharmacokinetic properties in the living brain is of value in localizing its action in the brain. Pharmacokinetic measurements in different anatomical regions of the human brain are not yet available. Limited pharmacokinetic measurements in rat brain subvolumes have been performed using atomic absorption technique. However, a noninvasive way of estimating the pharmacokinetics in different regions of the brain where the drug exerts its beneficial effects would allow such methods to be used in the study of patients undergoing Li therapy. Earlier (7)Li MR studies on rat brain regions have provided preliminary pharmacokinetic information from the whole brain. Using (7)Li MR spectroscopic imaging (SI) technology, Li distribution in brain regions of the rat at therapeutic dosages has been recently demonstrated by us. Here we report feasibility of local pharmacokinetic measurements on brain regions obtained by magnetic resonance SI technology. Our results suggest that Li is most active in a region stretching from the anterior cingulate cortex and striatum to the caudal midbrain, with greatest activity including the preoptic area and hypothalamic region. Some activity was seen in prefrontal cortex, but only minimal amounts in the region of the cerebellum and metencephalic brainstem.