The pharmacology of lithium will be studied in detail in normal man and in patients with essential hypertension, and with chronic renal insufficiency. Standard short-term renal clearance techniques will be utilized following the ingestion of a single small dose of lithium carbonate by each participant prior to study. The effects of lithium on the excretion of sodium, potassium, calcium and magnesium will also be investigated in rats. In addition, the effects of extracellular fluid volume expansion, diuretic-induced extracellular volume contraction, and parathyroid hormone, on lithium excretion will be studied. Methods of accelerating urinary lithium elimination will be explored with a view toward developing a therapeutic approach for patients with lithium intoxication. Lithium excretion will also be studied in patients with essential hypertension, and in others with mild-to-moderate chronic renal insufficiency, in order to determine if lithium might pose especial hazards, if ultimately employed for the treatment of psychiatric disorders in these patient groups.