Urinary excretion of homovanillic acid (HVA), the major terminal metabolite of dopamine, was not significantly different in patients with Parkinson''s disease as compared with control subjects in a similar age group. The excretion of HVA following the administration of reserpine and 3, 4-dihydroxyphenylalanine (DOPA) was likewise similar in both groups. In addition, no significant clinical effect was apparent after drug administration in either group. It is concluded that there is no abnormality in the over-all metabolism of dopamine in patients with Parkinson''s disease, although the possibility of a local aberration of the metabolism of this catecholamine in the corpus striatum cannot be excluded.