Estimation of catecholamines in human plasma was made by ion-exchange chromatography coupled with fluorimetry. Catecholamines in deproteinized plasma were adsorbed onto Amberlite CG-50 (pH 6.5, buffered with 0.4 M phosphate buffer) and selectively eluted by 0.66 M boric acid. The catecholamine fraction was separated further on a column of Amberlite IRC-50 which was coupled with a device for the automated performance of the trihydroxyindole method (epinephrine and norepinephrine) or the 4-aminobenzoic acid-oxidation method (dopamine). One sample could be analysed within 25 min with either method. The lower detection limits were 0.02 ng for epinephrine and dopamine, and 0.04 ng for norepinephrine. Plasma catecholamine contents of healthy adults at rest were epinephrine 0.07 +/- 0.01 ng/ml (n = 19), norepinephrine 0.27 +/- 0.03 ng/ml (n = 19) and dopamine 0.22 +/- 0.03 ng/ml (n = 26). The procedure of adsorption and elution of the plasma catecholamines by ion-exchange resin was simple, the simplicity contributing to constant recovery. The catecholamine fraction could be analysed without evaporation of the eluate. The analytical column could be used for the analysis of more than 1000 samples before excessive back-pressure developed. Our method of continuous measurement of plasma catecholamine fulfils clinical requirements.