Brain phosphorus metabolism was measured in 22 patients with depressive disorders. Ten of them had DSM-III-R bipolar disorder, and 12 had major depression. In bipolar patients, phosphomonoester (PME) and intracellular pH were significantly increased in the depressive state than in the euthymic state, while those values in the euthymic state were significantly low as compared to age-matched normal controls. Phosphocreatine (PCr) was significantly decreased in severely depressed patients compared to mild depressives. These findings suggest that high energy phosphate metabolism, intracellular pH and membrane phospholipid metabolism are altered in depressive disorders.