The lung ball is a special type of pulmonary aspergillosis (PA) occurring often after chemotherapy for leukemia. Histologically the ball, with air crescent sign on roentgenogram, is compatible with necrotizing lung tissue admixed with Aspergilli. The lung ball differs entirely from the common "fungus ball" in its quality, though they are similar in roentgenological appearances. The present two cases were leukemia which showed pulmonary findings in their therapeutic course, resulting in lung resection. In both cases the lung ball was confirmed histopathologically. Immunostaining of the lung tissue for neutrophil elastase showed elastase in various sites in the bronchial wall, pulmonary blood vessels (artery, vein) and cavitary wall. In our previous studies, much importance was attached to the disturbance of the pulmonary circulation caused by fibrin deposition as a factor in the developmental course of the fungus ball type aspergillosis (semi-invasive type). The circulatory disturbance of the lung was recognized also in the present cases. This two-way destruction of the pulmonary tissue, resulting from both neutrophil elastase activities and pulmonary circulatory disturbances, were regarded as the most important factor for the development of the lung ball. There are few studies on aspergillar lung ball with regard to the above respects.