We report a sensitive fluorimetric method, in which catecholamines are concentrated from plasma by liquid-liquid extraction and derivatized with the selective fluorescent agent 1,2-diphenylethyl-enediamine prior to chromatography. Optimal conditions for extraction, derivatization and chromatography were investigated. With alpha-methylnorepinephrine as internal standard, the chromatographic separations are complete within 6 min. Limits of detection are 0.3 pg for norepinephrine and epinephrine and 0.5 pg for dopamine. Coefficients of variation are low (3-7%). Comparison of plasma catecholamine values determined with this method and with an established method with electrochemical detection (n = 135) shows good correlation (r = 0.94-1.00), and regression lines are close to lines of identity.