The purpose of this study is to find out whether hypercalcemia and hyperparathyroidism are rare or not in manic-depressive patients taking lithium carbonate. The subjects were 13 patients receiving lithium and 19 healthy subjects not receiving it as normal controls. Serum ionized calcium (Ca++), serum parathyroid hormone (PTH), urinary calcium and cyclic AMP(cAMP) were measured. Cervical ultrasonographic examination was also performed. The mean serum Ca++ level in the lithium administered group was significantly higher than that in the control group (P < 0.02). There was no significant difference between the serum PTH levels in the two groups. The mean urinary calcium level in the lithium administered group was below the normal range, but the mean urinary of cAMP level was within the normal range. Although a parathyroid cyst was found in one lithium administered patient on ultrasonographic examination, no swelling of the parathyroid gland was observed in the other patients in the lithium administered group or in any of the control subjects. In the present study, no distinct hyperparathyroidism was found in the patients in the lithium administered group. Lithium administration affects calcium metabolism in manic-depressive patients and hypercalcemia seems to be one of the complications needing attention at the time of lithium administration.