Dopamine-B-hydroxylase (DBH, EC 1.14.17.1) is a copper containing enzyme that catalyzes the synthesis of norepinephrine in the sympathetic nervous system. DBH inhibitors have been used to treat hypertension in man. Quantitative studies of the interaction of DBH with its inhibitors using spectroscopic techniques such as electron paramagnetic resonance (epr), electronic absorption, fluorescence emission, nuclear magnetic resonance (nmr) spectroscopy are proposed. These studies will elucidate the mechanisms involved in the short term regulation of DBH and norepinephrine biosynthesis.