An automated catecholamine analyzer was assembled from a high-performance liquid chromatograph, an autosampler and an air segmented reactor equipped with a sensitive fluorometer. The trihydroxyindole technique was applied to the fluorometric reactor. Urine, plasma and brain homogenate were usually purified on an alumina column prior to high-performance liquid chromatography (HPLC). Centrifuged urine and a supernatant of brain homogenate can, however, be injected onto the HPLC column without further pre-treatment. The measurement of noradrenaline and adrenaline in plasma of a man at rest required 0.5--1 ml samples. Approximately 100 alumina eluates from urine can be treated per day when the analyzer is operated continuously.