METHODS Experiments were carried out on six unanaesthetized dogs fasted for 18-24 hr. Blood samples were takenfrom the antebrachial cephalic vein at regular intervals for glucose determinations by the micro method of Hagedorn & Jensen (1923). AU] dogs received 2 mg./kg. hexamethonium alone, 04 unit/kg. insulin alone, and insulin plus hexamethonium in these doses. Inaddition, hexamethonium, in a dose of 5 mg./kg., was given in a number of experiments. AUl drugs were given intravenously, insulin being given 5 min. before hexamethonium if both were administered in the same experiment. The sequence ofdrug administration was randomized. Hexamethonium was given as the iodide.