The prognostic value of electrocochleography and of the glycerol dehydration test in Meniere's disease is well recognized. Abnormal electrocochleographic waveforms carry a poorer prognosis. After adequate dehydration, significant threshold changes for better or worse predict the likely course of events following endolymphatic sac surgery.Meniere's disease frequently becomes bilateral. Vestibular aqueduct tomography in patients with Meniere's disease gives very different results, in both ears, compared with those in control patients. The acetazolamide cochlear hydration test can help detect latent hydrops. Plasma osmolality studies are an essential part of all these tests.Otoadmittance investigations show significantly higher baseline values in fluctuant endolymphatic hydrops compared with nonfluctuant Meniere's disease or control subjects. When the hearing improves after dehydration there is a paradoxical increased resistance to the flow of sound energy through the inner ear. Reduced hearing after glycerol is associated with an increase in maximum conductance or a decreased cochlear resistance. Otoadmittance studies on the “normal” ear of patients with “unilateral” Meniere's disease show similar abnormalities and changes.A study of serum levels of immune complexes and complement in patients with Meniere's disease shows elevated levels compared with controls. As yet the significance of this finding is unclear, though it may be related to disease activity.