A fluorimetric procedure for determining urinary adrenaline is described. This procedure eliminates the nonspecific blank occurring in the older methods to the extent that the levels obtained for urines collected under well defined physiologic states, such as sleep, moderate exercise and rest approach values obtained by bioassay as reported in the literature. The salient features of the method include a rigid control of pH at two critical steps, the addition of the standard to an aliquot of urine to correct for loss in processing and quenching, dilution of the sample to a point where quenching is minimal, and an optimal oxidation with MnO2 which destroys nonspecific fluorescent compounds without influencing the conversion of adrenaline to adrenochrome. Submitted on July 7, 1958