Analysis of plasma catecholamines (norepinephrine, epinephrine and dopamine) by high-performance liquid chromatography using 1,2-diphenylethylenediamine as a fluorescent reagent is described. We have developed an automatic catecholamine analyser, based on pre-column fluorescence derivatization and column switching. The analysis time for one assay was 15 min. The correlation coefficients of the linear regression equations were greater than 0.9996 in the range 10-10,000 pg/ml. The detection limit, at a signal-to-noise ratio of 3, was 2 pg/ml for dopamine. A new method of sample preparation for the pre-column fluorescence derivatization of plasma catecholamines was used. In order to protect the catecholamines from decomposition, an ion-pair complex between boric acid and the diol group in the catecholamine was formed at a weakly alkaline pH. The stabilities of plasma catecholamines were evaluated at several temperatures. After complex formation, the catecholamines were very stable at 17 degrees C for 8 h, and the coefficients of variation for norepinephrine, epinephrine and dopamine were 1.2, 4.2 and 9.3%, respectively.