We describe a "high-performance" liquid-chromatographic method for measuring picogram amounts of norepinephrine and epinephrine simultaneously in human plasma. Alumina-treated samples are injected onto a strong cation-exchange column (Zipax SCX) for the separation of catecholamines, with a sodium phosphate buffer/acetonitrile mixture as mobile phase. The separated catecholamines then enter a continuous-flow system and the reagents for the trihydroxyindole reaction are added sequentially; the fluorescent products are then measured with a spectrofluorophotometer. Analytical recoveries from plasma averaged 66% for norepinephrine, 68% for epinephrine. Amount and response (peak height) were linearly related up to 1000 pg. For catecholamines in human plasma, within-run and day-to-day CV's were 0.2% and 1.0%, respectively, for norepinephrine, and 0.3% and 0.9%, respectively, for epinephrine. Average values for norepinephrine and epinephrine in apparently normal human plasma were 185 +/- 29 ng/L and 32 +/- 8 ng/L, respectively (mean +/- SEM, n = 10). This relatively rapid and highly sensitive system is suitable for routine use.