With the more widespread use of sensitive specific methods of measurements of catecholamines and metabolites, more emphasis must be given to assessment of dynamic indices of catecholamine turnover. Wide inter-individual differences in noradrenaline clearance from plasma and in resting endogenous production rate, together with individual differences in responsiveness, frustrate simplistic attempts to relate plasma level of transmitter with turnover. To assess catecholamine function adequately plasma and urinary levels of catecholamine and the main metabolites should be determined together with an index of responsiveness. Central nervous catecholamine turnover cannot be easily assessed from measurement of urinary metabolite excretion Cerebrospinal fluid concentration of MHPG may provide an index of brain noradrenaline turnover.