To investigate the placebo effect in surgery for Ménière's disease, a double-blind controlled study was undertaken, comparing effects of a regular endolymphatic shunt with those of regular mastoidectomy. Thirty patients with typical Ménière's diseases, selected because of unsuccessful medical treatment, participated. Patients completed daily dizziness questionnaires three months before and 12 months after surgery, with registration of nausea, vomiting, vertigo, tinnitus, hearing impairment, and pressure in the ears. Patients were operated on at two universities, and the patients operated on at one underwent controlled study each month at the other. At termination of the trial, both investigators and patients gave their opinions of the efficacy of the operations. Minor differences were seen between active and placebo groups, but the greatest difference in symptoms was found when preoperative and postoperative scores were compared: both groups improved significantly