Pharmacological studies of the pupils of 7 patients with familial amyloid polyneuropathy (FAP) were performed in order to demonstrate the site of the lesion. Supersensitivity to 1.25% epinephrine was observed frequently, but not to 2.5% methacholine. The lesions of the sympathetic nervous system, judging from the epinephrine and tyramine tests, were regarded as preganglionic in 2 patients and postganglionic in 4. Among 3 patients reexamined six months later, 1 had developed signs of sympathetic postganglionic disturbance and another showed a peripheral parasympathetic disturbance associated with progress of a sympathetic preganglionic disturbance. From these results it was suggested that in FAP, sympathetic abnormalities involve the pupils more often than parasympathetic disturbances, and pharmacological studies can detect the autonomic dysfunction before it becomes clinically apparent.