A study was made of brainstem auditory evoked potentials (BAEP) in 66 patients from 56 families with different forms of spinocerebellar degenerations (SCD). 27 patients with olivopontocerebellar degeneration (OPCD), 13 patients suffering from Friedreich's disease (FD), 10 patients with Pierre Marie's familial ataxia (PMFA), 6 patients with late onset cerebellar atrophy (LOCA), and 10 patients with other forms of SCD were examined. The changes in BAEP turned out extremely diverse which can be regarded as a manifestation of marked phenotypic pleomorphism common to SCD. The most considerable changes in BAEP were discovered in FD and OPCD, whereas the least marked ones in PMFA and LOCA. The character and degree of BAEP disorders reflect the spreading and gravity of degenerative alterations in the brain stem in different forms of SCD. The authors discuss the possibility of the use of BAEP for objective estimation of the gravity and spreading of the pathological process as well as of the electrophysiological control over its course in SCD patients.