As a mood-stabilizing agent, lithium has a long history of documented efficacy as well as risks associated with its use. Relative to other psychiatric medications, lithium exhibits a number of unique pharmacokinetic properties. The use of in vivo nuclear magnetic resonance spectroscopy of the 7Li isotope has immense potential to provide an improved understanding of the pharmacokinetic basis of lithium response and nonresponse. The conventional use of orally administered immediate-release preparations of lithium salts in psychiatry is associated with high postabsorptive blood lithium concentrations and trough lithium concentrations in later phases of lithium elimination. These ups and downs of blood lithium concentrations are associated with acute lithium toxicity and symptomatic states, respectively. The use of slow-release lithium formulations represents a long available means of diminishing the postdose variation in serum lithium concentrations. A significant need exists for head-to-head comparisons of the pharmacokinetics and clinical response relationships for slow-release and immediate-release lithium formulations.