Abstract
The guinea pig lateral superior olive was examined immunocytochemically using antisera against enkephalin and choline acetyltransferase sequentially on the same sections. A colocalization of choline acetyltransferase-like and enkephalin-like immunoreactivities was found in cells of the lateral superior olive that give rise to the lateral system of olivocochlear efferents. Only choline acetyltransferase-like immunoreactivity was observed in the group of olivary nuclei that give rise to the medial group of olivocochlear fibers.