Application of various mildly irritant substances to the posterosuperior and anteroinferior aspects of the external auditory canal of the rabbit, with intact ear drum and middle ear, produced cholesteatomas in the skin of the auditory canal, and the tympanic membrane particularly in the pars flaccida. At the anteroinferior insertion of the tympanic membrane, however, cholesteatoma growth could not be induced in these animal experiments. In severe diffuse otitis externa, secondary to the operative closure of the external auditory canal, cholesteatomas also preferably develop in the pars flaccida, the relatively thick, loose intermediate layer of connective tissue allows a rapid expansion of epithelial ridges thus favouring the formation of cholesteatoma in this region.