Meniere's disease can only be studied in patients, since it does not occur spontaneously in animals nor can it be induced in them. However, aspects of the disease such as endolymphatic hydrops can be usefully studied in animals. A study of the natural history (epidemiology) of Meniere's disease demonstrated the three major symptoms (triad) to be vestibular symptoms, auditory symptoms, and aural pressure. Bilaterality occurs in at least one out of 3 patients, and may approach 50% over full lifespans. Aural pressure (74.1%) was common, as was positional vertigo (85.9%) during and/or between attacks. Clinical variants such as vestibular Meniere's disease could persist for 25 years or more. Understanding the pathogenesis of Meniere's requires a study of known and unknown causes. In this study, Meniere's disease (cause unknown) was differentiated from Meniere's syndrome (cause known). Meniere's disease or syndrome can occur years after some inciting cause; thus all forms of Meniere's can be considered to have a delayed onset. Meniere's syndrome can occur as a sequel to syphilis, otosclerosis, infection (for example otitis media), or trauma. Endolymphatic hydrops explained on the basis of quantity and quality of endolymph is found in all forms of Meniere's disease and syndrome. Representative cases and pathological examples are discussed. Hydrops of the pars inferior (cochlear duct and saccule) is the most important finding in Meniere's disease. In some (but not most) cases, ruptures of the membranes are seen. The saccule can distend into the lateral semicircular canal. Symptomatic attacks are explained on the basis of both physical and biochemical phenomena. This study discusses concepts of pathogenesis of the disease, finding both theories of longitudinal (slow) and radial (fast) flow to be operational. Longitudinal flow, however, appears to be more important than radial flow, especially in advanced Meniere's where perilymph in the scala vestibuli and vestibule disappears and is replaced by membranous labyrinth. Meniere's disease (idiopathic) and Meniere's syndrome (cause known) probably occur as a result of endolymphatic absorptive dysfunction (the site being endolymphatic duct and sac). Hypocellularity of the mastoid and periaqueductal air cells, hypodevelopment of Trautmann's triangle, and anterior displacement of the lateral sinus are likely to be important findings associated with developmentally dysfunctional absorption of endolymph.(ABSTRACT TRUNCATED AT 400 WORDS)