An automated trihydroxyindole method for the determination of noradrenaline and adrenaline is described. Samples are analyzed at the rate of forty per hour, compared with twenty per hour for the previously described semiautomated methods (13, 14). The method is more sensitive than the latter two, and therefore tha concentration of the individual amines present in a sample can be determined by the differential spectral technique of Cohen and Goldenberg (10). Tracer amounts of tritium-labeled noradrenaline or adrenaline are added to the samples, and the efficiency of the isolation process calculated from radiochemical analysis of the ion-exchange column eluate. The method has been applied to the determination of the amines in tissues, urine, and plasma, and the results obtained are in agreement with those reported by other workers using manual methods.