The aetiology of Menière's disease (MD) remains obscure, but is likely to be multifactorial, one of the factors being a genetic predisposition. Forty-one families with more than one living member with MD were ascertained and affected and normal relations examined. Blood was collected and DNA extracted and stored. In these families the mode of inheritance is autosomal dominant, the penetrance of the mutation being about 60 per cent. Some of the family members exhibit a partial syndrome, vestibular symptoms predominating. Sporadic and familial cases exhibit the same clinical features. The striking finding is the phenomenon of anticipation, whereby with successive generations there is an earlier age of onset and a tendency to more severe manifestation. The inference, considering that the cells which regulate endolymph are of neuroectodermal origin, is that, like other neurodegenerative disorders which show anticipation, MD manifestation is likely to be related to trinucloetide expansion within a gene.