Brain stem electric responses (BSER), evoked by acoustic stimuli, were investigated in 29 patients with multiple sclerosis and compared with the responses in a control group of 26 young adults without neurological disease or hearing defect. The procedure included monaural and binaural stimulus presentation of single clicks and pairs of clicks. In the evaluations the vertex-positive Jewett I, III and V response components, and the vertex-negative "FFP7" peak were considered. In the assessment of the BSER components, the FFP7 (the vertex-negative 7 ms far field potential following the JewettV wave) proved to be the best single component with respect to reproducibility in normal subjects. In addition the FFP7 was the single most consistently abnormal component in the patient group. Determination of the latency of the Jewett components and the interpeak conduction times, however, contributed further to the disclosure of the abnormal cases. Five of the patients whose hearing was impaired were considered separately. Of the remaining 24 patients, 20 (83%) had BSER abnormalities. Further analysis did not reveal a clear correlation between BSER abnormalities and clinical signs of brain stem dysfunction.