The effect of the ergot derivative bromocriptine (5 mg orally) on blood pressure and plasma catecholamine concentrations was explored in normal volunteers. A significant decrease of plasma noradrenaline was found, while dopamine and adrenaline concentrations did not change significantly. Systolic and diastolic blood pressures were significantly lowered at 150 min after administration. The hypotensive effect of bromocriptine seems to be mediated by a lowered release of noradrenaline from sympathetic nerve endings. It may be hypothesized that the drug stimulates presynaptic dopamine receptors located on postganglionic sympathetic nerves, thus inhibiting noradrenaline discharge.