A sensitive and specific direct analysis of urinary normetanephrine (NMN) and metanephrine (MN) was achieved utilizing reversed-phase high performance liquid chromatography and electrochemical detection. Individual specimens from "control" subjects and those with pheochromocytoma were hydrolyzed and the metanephrines separated from other urinary constituents by elution with ammonia from a Dowex CG-50 resin. Chromatographic peaks were identified by retention behavior, co-chromatography with reference compounds, ratio of responses at various oxidation potentials and stopped-flow UV spectra of the collected fractions. The NMN and MN content for the control subjects was between 0.086 and 0.21 (mean = 0.14) μg/mg creatinine and 0.012 and 0.092 (mean = 0.039) μg/ mg creatinine, respectively. The values for subjects with pheochromocytoma varied from 1.5 to 27.5 (mean = 9.9) μg/mg creatinine for NMN and 0.10 to 1.60 (mean = 0.86) μg/mg creatine for MN. The patient with ganglioneuroma had an NMN of 4.1 and an MN of 0.80 μg/mg creatinine. While this method permits discrimination between those patients with pheochromocytoma and the overwhelming majority of hypertensive patients, it may ultimately be further extended to separate normal subjects from those with more subtle derangements in catecholamine metabolism.