A longitudinal sequential study of oval and round window changes in otitis media in an experimental animal (cat) using Eustachian tube obstruction was done. Thirty–two animals were used. In this first sequential study of the oval and round windows in otitis media, the continuum of round window membrane changes from 1 day to 6 months after obstruction revealed changes to be gradual and similar to those of the mucoperiostium. These changes are suitable for changes in permeability and suggest that this membrane is a very likely pathway from the middle to the inner ear. Bony fistulas were not observed and the oval window remained essentially unchanged in time, thus they were not considered routes into the inner ear. Other possible routes are discussed.