Summary.1A colorimetric method for quantitative determination of noradrenaline is described.2Determination of the oxidation rate at various pH for noradrenaline and adrenaline has shown that adrenochrome formation is complete after 1½ minutes at pH 4 whereas only some 10 p. c. of the maximal amount of noradrenochrome has been formed during the same time at pH 4. Noradrenochrome formation is complete in 2 minutes at pH 6.3For routine determination adrenaline was oxidized at pH 4 for 11/2minutes and noradrenaline at pH 6 for 3 minutes. Before removing excess iodine with thiosulphate the reaction may be adjusted to pH 4, where the bleaching effect of excess thiosulphate was minimal.4A method for differential determination of adrenaline and noradrenaline depending on the different oxidation rates at pH 4 and 6 for the two substances is described. This method has been successfully applied to suprarenal extracts.5The greater stability of noradrenaline in solution against oxidation as compared with adrenaline appears to be of practical value for example in solutions of local anaesthetics