In view of recent controversies concerning the preservation of hearing in acoustic neurinoma surgery, we examined the courses of the vestibular and cochlear nerve fibers in 12 intact acoustic neurinomas studied in our department. Due to its lack of specificity, the Luxol fast blue stain was found to be inadequate for our study of the nerve fibers. In contrast, Verhoeff's stain proved to be satisfactory when combined with a highly specific immunohistochemical technique. There were macroscopically visible adherences between the tumor and the cochlear nerve in 9 out of the 12 specimens. From those specimens, histological sections were obtained in which both the cochlear nerve and tumor could be clearly identified. In these specimens the cochlear nerve was involved in the tumoral process and there was no clear cleavage plane between the nerve and the tumor. However, all these patients suffered only from minimal losses of hearing as a result of their tumors.