1. Following the injection of adrenaline into rats pre‐treated with thyroxine, there is a pronounced and prolonged increase in their oxygen consumption. On this basis a method is described for following increases in the rate of secretion of adrenaline in response to physiological stimuli in rats.2. Using this method the onset and the cessation of the increased rate of secretion of adrenaline during insulin induced hypoglycaemia has been found to correspond to a blood glucose concentration of approximately 40 mg/100 ml.3. 3‐Methylglucose (3‐O‐methyl‐ D‐glucopyranose) is shown to cause a marked and sustained increase in the blood glucose concentration.4. This action of 3‐methylglucose can be accounted for by an increase in the rate of secretion of adrenaline, as it is accompanied by a rise in oxygen consumption in thyroid treated rats and is prevented by interruption of the central nervous connexions of the adrenal medulla.5. These findings can be explained by 3‐methylglucose's acting upon the receptor which reacts to insulin hypoglycaemia by bringing about the secretion of adrenaline. It is shown that the effective stimulus to this receptor is not a low blood glucose concentration. The stimulus is possibly a depressed rate of utilization of glucose by the receptor tissue.