Perilymph fistula, pathologic leakage of perilymph from the otic capsule, is caused by numerous conditions, many of which are unknown. Such fistulas need special attention concerning their early diagnosis, treatment and differential diagnosis, for they can cause a sudden loss of hearing and other hearing and vestibular function defects. Though exploratory tympanotomy reveals leakage of perilymph fluid, diagnosis of this condition is far from easy. The authors performed this study for the basic studies of the site and shape of perilymph fistula. Healthy albino guinea pigs, weighing a average 400 gm, with normal Preyer auricular reflex were used. Under Nembuthal anesthesia, postauricular incision was made exposing the bullae, and a micropore was made on the basal turn of cochlea. A microcatheter filled with artificial perilymph fluid was inserted and then fixed into the scala tympani connected to a pressure measuring system and infusion pump. The leakage site was verified by gradual pressure increment on the infusion pump. 1) Of the 16 cases, 2 cases were from the oval window and 14 cases from the round window. 2) In the cases of oval window fistula, fistulas were seen in anteroinferior and posteroinferior portion of the annular ligament. 3) In the cases of round window fistula, fistulas were most seen in the inferior margin. 4) Slit-shaped fistulas were most common in the round window.