If such tumours release insulin to the blood, it could explain the rare and unexplained occurrence of hypoglycaemic attacks described in a few patients with phaeochromocytoma (3, 4, 5, 6); in at least two of them, the hypoglycaemic attacks were hyperinsulinaemic (4, 5) and one was cured from such attacks by removal of the tumour (5). This evidence concerns the gene INS and pheochromocytoma.