Methoxynorepinephrine is a catecholamine metabolite that can be measured in serum or urine. Elevated methoxynorepinephrine can be seen in patients with pheochromocytoma, which may be more serious, and consultation with a physician is recommended for diagnosis and treatment. Pheochromocytomas originate from pheochromocytes in the adrenal medulla or in the parasympathetic ganglia of the sympathetic and parasympathetic nerves outside the adrenal glands. The incidence of malignant pheochromocytoma is less than 10% and the tumors are often very large. Signs of malignancy are metastasis and peripheral tissue invasion, and cancerous thrombus formation in blood vessels and lymphatics. Patients with pheochromocytoma usually require surgery. For patients with malignant pheochromocytomas that do not tolerate surgery, or have failed to be resected, or if the tumor recurs after surgery, drugs such as alpha-adrenergic receptor blockers may be used to improve symptoms, as well as iodine 131-mesoiodobenzylguanidine endoradiotherapy. High methoxynorepinephrine can also be caused by other reasons, the occurrence of high methoxynorepinephrine is recommended to go to the hospital, ask the doctor to judge and deal with.