Single doses of glucagon and zinc glucagon were administered to fed rabbits and changes in blood glucose and total blood amino acids were measured. The concentration of amino acids was depressed longer with zinc glucagon (about 30 per cent decrease for at least twelve hours) than with glucagom. A satisfactory laboratory method for comparingthe duration of action of preparations of glucagon was developed. Quantitative analyses showed that all of the common amino acids in plasma were depressed by zinc glucagon. Although 3.1 moles of nonessential amino acids were removed from the peripheral circulation for every mole of essential amino acid, no statistically significant difference between the two classes of amino acids was found. The over-all reduction of blood amino acids may be largely a reflection of the gluconeogenic action of glucagon, but the variations observed among the amino acids leave doubt that the underlying mechanism involves a uniform induction of gluconeogenic enzymes; other catabolic effects of glucagon on amino acids must also be considered.