The possibility of central and peripheral impairment of the acoustic analyser was studied in 18 patients with severe diphtheritic polyneuropathy (DP) using brainstem acoustic evoked potentials (BAEPs). The acoustic nerve impairment was found in 27.8%, the central abnormalities--in 44.4%. All the patients with CNS impairment suffered from chronic alcoholism. The data obtained have been compared to those of 26 patients with chronic alcoholism. In this group, peripheral polyneuropathy was confirmed in 76.9% cases; BAEPs revealed isolated involvement of the peripheral part of the acoustic nerve in 7.7% and CNS impairment was found in 84.6% patients. The results of the study suggest that diphtheritic toxin is not implicated in CNS lesions. Central changes found in the BAEPs analysis were related to chronic alcohol intake and did not aggravate diphtheria course.