This is a report on four cases of atelectasis which were implicated as one case of mucoid impaction and three cases of blood clots in main bronchus. The 1st case was found to be massive atelectasis on Lt. entire lung due to mucoid impaction with pulmonary tuberculosis. This case was performed the Lt. pneumonectomy. There are contain-ing impacted yellowish-gray jelly like thick materials on the Lt. whole bronchial trees and pathologic findings were consistent with tuberculosis including caseation necrosis and multinucleated giant cell on whole left lung thoroughly in microscopic findings. The 2nd and 3rd case [25 years old female and 30 years old female] were diagnosed as one sided entire lung ateletasis which were led by accumulation of old blood clots on bronchus following incomplete expectoration of sudden massive hemoptysis from pulmonary tuberculosis lesion. These two cases were recovered by removal of blood clots and bronchial irrigation under bronchoscopy. Follow up chest film revealed well aeration. The 4th case [45 years old] was taken the removal of old blood clots and tissue debris under the bronchoscopy as bronchial obstruction following massive hemoptysis. The cytologic findings revealed the class III in fresh sputum and class 1V in bronchial irrigation which may suggest of malignancy. However, we could not found the causative lesions suggestive malignancy by the bronchography and other diagnostic measurements.[KTCS 1973;1:41-46]