Membrane rupture has been implicated as one of the causes of sudden sensory hearing loss, and cases are reported in the world literature in which an improvement of hearing could successfully be obtained by closure of the fistula done upon confirming it surgically. While a direct external force (trauma, atmospheric pressure changes, coughing, etc.) is a likely cau se of membrane rupture, 'so-called sudden deafness' is claimed to be associated with the presence of membrane rupture whose dynamic mechanism is not fully understood yet.On the other hand, reports made so far on sensory hearing loss caused by membrane rupture are quite limited in number in Japan, there being few purporting that surgery brought about an improvement of hearing. We, at our department, performed an exploratory tympanotomy for the treatment of 'socalled sudden deafness' in a 27-year-old male (whose hearing was impaired to the point of scale out on audiometry) in July 1977. At operation were noted findings presumptive of a perilymph fistula at the round window, closure of which a piece of fascia resulted in a prompt improvement of hearing. A careful scrutiny of this case disclosed that (1) the patient was fatigued just before the onset of disease and (2) there was a progressive worsening of hearing loss. In another case of barotraumatic membrane rupture the onset of disease ccurred with aural stuffiness after diving in January 1979 and the patient's hearing was lost to the level of scale out on the 7 th disease day closure of the rupture upon confirming the presence of a fistula in the inner ear at operation resulted in an improvement of hearing.