Noradrenaline synthesis and metabolism of dopamine was evaluated in three patients with familial dysautonomia and compared with that of six normal subjects. Each patient and subject was infused with 104.8 μCi of dopamine-2-¹⁴C dissolved in 1000 ml of physiological saline. The urine was collected during the infusion period and at intervals thereafter. Using a specially designed flow monitor system, the various biosynthetic and metabolic products of dopamine were separated, identified, and their radioactivity measured. The results indicate that in familial dysautonomia the synthesis of noradrenaline is significantly decreased; this is reflected by a decrease in recovery of radioactive noradrenaline as well as various metabolic products of noradrenaline, i.e. 3-methoxy-4-hydroxymandelic acid (MOMA), normetadrenaline, and normetadrenaline conjugate. Concomitant with this decrease in noradrenaline synthesis, there was a shift towards dopamine metabolism as reflected by an increase in the recovery of primary and secondary dopamine metabolites; 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxy-4-hydroxyphenylacetic acid (HVA), 3-methoxytyrosine, and respective conjugates, etc. Whereas all dysautonomic patients showed the same general metabolic pattern as was expected, they varied in degree.