Sympathetic skin responses (SSRs) were abolished in 4 patients affected with fatal familial thalamic degeneration involving the anterior (A) and dorsomedial (DM) thalamic nuclei, without lesions of the peripheral vegetative system. Abnormalities of SSR were not due to peripheral nerve lesions. It is concluded that SSR integrity also depends upon thalamic formations ("visceral" thalamus) and their frontal cortical connections.