The effect of nasal obstruction on the nasal and middle ear mucosa was studied on 138 albino rats with unilateral and bilateral nasal obstruction for variable periods up to 3 months . Group 1 was composed of 100 rats which were subjected to unilateral nasal closure . They were divided into 5 equal subgroups and were sacri¬ficed after variable periods so as to study the histological changes of the nasal and ear mucosa . Group II was composed of 38 rats, these being subjected to bilateral na-sal closure.These had died within 9 days. The nasal mucosa of the open side showed squamous metaplasia