The aim of the study was to validate a HPLC-ED (Electrochemical Detection) method for the determination of methanephrine and normethanephrine in blood plasma and to to compare the obtained data with those published previously. The ability of the proposed method to distinguish the patients with and without pheochromocytoma has been proved and the results have been compared with the HPLC-FLD (Fluorescence Detection) determination of free catecholamines in urine.