Chorda tympani nerve specimens of 10 patients were studied by the light and electron microscope. The nerve specimens were obtained while performing stapedectomy in 7 patients, a tympanoplasty in two patients with otitis media chronica, and from one patient whodied 8 months after hemiglossectomy, neck-dissection and radiotherapy because of squamous cell carcinoma. The chorda tympani nerve is built up by few 10 to 12 micron thick and numerous 3 to 4 micron thick myelinated fibers in the semithick sections. The 10 to 12 micron axons are largely reduced in patients with chronic middle ear infection and in older patients. In persons with otosclerosis degenerative alterations of the axons and inclusions in the cytoplasm of the Schwann cells can be demonstrated similar to those of the diabetic, alcohol induced and ischemic neuropathy. In patients with chronic middle ear disease the degenerative changes mainly occur in the myelin sheats and in axoplasma finally leading to axolysis. A total degeneration and fibrous transformation of the chorda tympani nerve can be observed after hemiglossectomy. By means of morphological criteria afferent and efferent axons can not be distinguished in this material.