This report summarizes new techniques for examining aspects of sympathoadrenomedullary function. Tracer pharmacokinetic methods are more accurate than measurements of antecubital venous norepinephrine (NE) in assessing sympathoneural responsiveness. During mental challenge (playing a video game), patients with essential hypertension had significantly larger increments of NE spillover into arterial blood than did normotensive control subjects, whereas responses of antecubital venous and even arterial NE did not differ significantly between the groups. The rate of neuronal reuptake of endogenous NE can be measured in vivo using plasma levels of NE and of the intraneuronal NE metabolite, dihydroxyphenylglycol (DHPG). Regional production of dihydroxyphenylalanine (DOPA) may reflect catecholamine biosynthesis, and DOPA may be an indirectly acting natriuretic neurohormone. Positron emission tomography after injection of positron-emitting fluorodopamine may allow in vivo, noninvasive assessments of regional sympathetic function.