Necropsy studies were done on six patients with idiopathic paralysis agitans, one with multiple system atrophy including features of Parkinsonism, and one control. Autonomic functions had been evaluated during life to a varying degree. Intra-arterial blood pressure studies were carried out on two patients with paralysis agitans (cases 4 and 6) and the one with multiple system atrophy (case 7). Lewy bodies with or without cell loss were seen in the sympathetic ganglia of five cases of paralysis agitans. Three of these had orthostatic hypotension and the severity of the lesion approximately correlated with the degree of hypotension. It is concluded that the lesions of the sympathetic ganglia may play a major role in the production of orthostatic hypotension in idiopathic paralysis agitans.