A patient with lithium-induced, vasopressin-insensitive diabetes insipidus was studied during two consecutive manic episodes that were successfully treated with lithium. Polyuria occurred several days after lithium-induced brain electrical changes were observed, and at serum lithium concentrations close to 1.0 mEq./liter. Polyuria began during a period of behavioral improvement and persisted after the manic symptoms subsided. Polyuria did not occur in association with serum lithium concentrations over 1.8 mEq./liter, and a fourfold increase in sodium intake did not reduce the polyuria. Chlorothiazide reduced polyuria and permitted the patient to continue the lithium treatment.Abstract Teaser