The study of hydrocarbonated metabolism in a newly born affected by leprechaunism is presented. Glycemia throughout the day and with a diet rich in carbohydrates (80 g/day) fluctuated between hyperglycemic (295 mg/dl) and hypoglycemic (37 mg/dl) figures. When ingestion of carbohydrates was reduced to half and the intake fractioned these fluctuations dissappeared. After a glucose overdose (3 g/kg IV) insuline figures were permantely high (from 315 IV/ml to 251 IV/ml). Exogen insulin test (0,1 IU/kg IV) did not reduce glycemia to an improtant level (time 0: 187 mg/dl; time 60: 129 mg/dl). The administration of glucagon (0.3 mg/kg did not normally raise glycemia (35, 54, 31 and 41 mg/dl in times 0', 30', 60 and 120'). In the studied case existed an intolerance to diets rich in carbohydrates, hyperinsulinism and lack of response to insulin and glucagon. Insulino-resistance seems to be of the peripheral type because neither elevated figures of antagonists nor presence of antiinsulin antibodies were detected and the response to exogen insulin was diminished. The underdevelopment of these patients seems to depend upon the alterations of the hydrocarbonates metabolism and the simple improvement of it by means of dietetic measures seems to be of great therapeutic value.