The response of patients with suspected Ménière's disease to the glycerin test was reviewed in a prospective evaluation covering a 10 year period. Three hundred and eighty three patients with 495 suspect ears were tested and were classified as to hearing improvement 3 h post-orally administered glycerin. Two hundred twenty-five patients (265 ears) were diagnosed as Ménière's disease. Sixty-six percent of these ears showed significant hearing improvement by pure tone threshold and/or speech discrimination measurements with the glycerin test. The test protocol developed and revised at the University of Washington provides a differential diagnostic means of identifying endolymphatic hydrops which is a specific and practical test. It is easily available as a routine office procedure.