In a specially designed animal model the penetration of glucocorticoid and oxytetracycline through the intact tympanic membrane was studied. Dogs were anesthetised for up to 8 h, and the substances were administered to the external auditory meatus. The measured concentration of the applied glucocorticoid in the tympanum showed a level which can be expected to be therapeutically active. When treating the inflamed middle ear, an adjuvant therapy with the combination dexamethasone-21-isonicotinate/oxytetracycline/natamycine/;etracain (Incut) should be taken into consideration. Although oxytetracycline was administered as well, this substance could not be measured in the small samples due to technical reasons. To find out about penetration of o%ytetracycline will have to be the object of another series of experiments.