We report the case of an elderly woman with severe dysautonomic orthostatic hypotension in whom a deficit in dopamine B hydroxylase has been established. In the literature, such a deficit has been described in six young adults with long standing symptoms of postural hypotension. This enzyme catalyses the conversion of dopamine to noradrenaline. In our elderly patient, noradrenaline and adrenaline were undetectable in the plasma, but plasma dopamine was detectable. Treatment with the synthetic amino acid, DL-threo-dihydroxyphenylserine, which is converted to noradrenaline by dopa-decarboxylase, resulted in a significant increase in blood pressure. The mechanism of this acquired deficit is not elucidated.