The method of Folin, Cannon and Denis (J. Biol. Chem. 1913, 13, 477.) for the estimation of adrenaline is found unsatisfactory when applied to the adrenal glands of rats and pigeons weighing about 0.03 gm., since, under the conditions adopted, the rate of fading and the tint of color of the adrenaline solution differ from those of the standard uric acid solution. Slight loss of color intensity, due to oxidation of adrenaline, takes place in the original method. Cold aqueous 10% trichloracetic acid solution is a satisfactory extracting agent. At any one temp., the time of maximum color production is the same for the various concentrations of adrenaline studied. Any one concentration of adrenaline gives the same color maximum, but after a time interval which decreases as the temp. rises. The cleaned glands are ground with 3 cc. of 10% trichloracetic acid and a little purified sand in a Pyrex test tube cut down to 1/2 size. The extract is filtered through a wad of cotton wool into a 25 cc. flask, tube and funnel washed first with distilled water acidified with trichloracetic acid solution. The flask is left for about 20 mins. in a thermostat at 20[degree]C, color reagents added and made up to 25 cc. with distilled water, transferred to cell of 2.35 cm. diameter, left for another 20 mins. in thermostat and the color is matched against the standard glasses of a Lovibond tintometer. The adrenaline content is obtained by reference to a calibration curve showing the color produced by various concentrations of pure synthetic adrenaline.