Four neuropeptides; cerebellin, corticotropin-releasing hormone (CRH), neuropeptide Y and somatostatin were studied by radioimmunoassay in the postmortem human brains obtained from three patients with olivopontocerebellar atrophy (OPCA) and one with Shy-Drager syndrome. Significant decreases in cerebellin and CRH concentrations were found in the cerebellar hemisphere of these diseases compared with controls. These findings suggest important pathophysiological roles of cerebellin and CRH in these cerebellar diseases. Such significant decreases were not found in neuropeptide Y and somatostatin.