The relative activities of adrenaline, noradrenaline and isoprenaline in producing hyperglycaemia, hyperinsulinaemia and glycogenolysis in liver and skeletal muscle have been studied in both fed and fasted rats. Independent of prandial state isoprenaline significantly elevates plasma insulin level. Noradrenaline has no demonstrable glycogenolytic action in the liver even at a dose of 1 mg/kg regardless to the prandial state. These observations suggest that in the intact organism enhanced insulin-secretory effect of isoprenaline counteracts and masks the glycogenolytic effect of this drug in the liver.