The low differential threshold (0.4 to 0.2 dB), together with incomplete speech discrimination (about 70%), raised ultrasound perception threshold (over 10 v); high frequency noise in the ear and vestibular hyporeflexia on the side to be operated upon appear to be unfavorable prognostic signs for stapes surgery in otosclerosis. Eighty-six percent of the patients showed an inner ear response to the operation; in 10.3% of patients there was an unfavorable form of traumatic labyrinthinopathy. To prevent postoperative labyrinthine reactions, controlled hypotension was introduced with the use of ganglionic blocking agents. Without controlled hypotension after the operation spontaneous nystagmus was noted in two thirds of patients: In the cases of controlled hypotension it occurred in one half of the patients. Vomiting was three times as frequent in the group without controlled hypotension.