The glycerol test is currently widely used to evaluate Menière's disease, particularly in regard to its suitability for decompressive surgical therapy. Our previous findings have shown that patients with Menière's syndrome respond extremely well to placebo treatment. We have investigated the effect of psychological factors in the outcome of the glycerol test. It was administered twice to each of a group of patients with a typical Menière's syndrome. On one occasion the patient was told the hearing would improve, and on the other that the hearing would worsen. The same dose of glycerol was provided for each test, but with a different flavor. The sequence of test was randomly applied. The audiologist was unaware of instructions given to the patient. The patients usually responded as instructed. These results are discussed with particular regard to the risk of patient selection for surgery.