The Weil-Malherbe and Bone method for the analysis of the plasma concentration of epinephrine and norepinephrine has been modified and used to determine the plasma concentration in normal humans. The average value for epinephrine in the plasma of men in this series was less than 0.11 µg./L.; for women it was 0.47 µg./L. The average value for norepinephrine in men was 3.4 µg./L. and in women it was 4.9 µg./L. The differences between the concentrations in men and women are significant, P<0.001 and P<0.01 for epinephrine and norepinephrine, respectively. Evidence has been presented to indicate the specificity of the method. Reproducibility and recovery data have been given.