Medium latency auditory evoked potentials (8-50 ms latency interval) are not yet established as an important diagnostic procedure. This is mainly due to the fact that the origins of the single components are not yet known. Components of the MLAEP were investigated and normal values were calculated in order to distinguish neurogenic and myogenic components. Based on this investigation the role of the MLAEP in clinical practice can be judged. Mean values (31 subjects) for ipsi- and contralaterally recorded potentials were calculated independently for recordings with and without myogenic contamination. The following components were measured: V, VI, VII, No, Po, Na, Pa, Nb. In addition sixteen patients with idiopathic facial paresis - consequently lacking the postauricular reflex - were investigated. Normal values of the myogenic component Po (when present) are presented to determine the so called "crossed acoustic response".