Survival period of malignant pheochromocytoma treated only conservatively is reported to be less than one year by T. Sato. A patient of malignant pheochromocytoma with liver metastasis has been treated with alpha-methyl-p-tyrosine (alpha MPT), tyrosine hydroxylase inhibitor, in the last 5 years. Catecholamine levels markedly decreased and he has a long survival time. He lives over 17 years from the detection of malignant pheochromocytoma. alpha MPT was considered to have a role to protect a patient from cardiomyopathy induced by hyper-catecholaminemia and to have the action of inhibiting the growth of this tumor. The growth of this tumor was very slow. Since this case had insulin independent diabetes mellitus, insulin therapy was applied, however, blood glucose level was not controlled well. Then we tried midaglizol (DG-5128), alpha 2-adrenoceptor antagonist, to control diabetes mellitus and a sufficient control was obtained. C-peptide level in urine was increased concomitant with decrease of blood glucose. This fact suggested that insulin secretion was improved. It is well known that catecholamine, especially noradrenaline has an inhibiting action on insulin secretion from beta cell. This action was appeared through alpha 2-adrenergic receptor. DG-5128 has an action as alpha 2-adrenoceptor antagonist. We think an inhibiting action on insulin secretion of catecholamine was diminished through its action as adrenoceptor antagonist. Kawazu et al. reported that catecholamine levels, heart rate and blood pressure did not change by DG-5128 administration in healthy subjects. In this patient, no change was appeared either. No major complication was observed during this treatment.