The radiological course of an echinococcus cyst of the lung before and after rupture is described, together with the cytological and histological findings. The resultant tissue changes and appropriate treatment (lobectomy) are discussed. In the presence of the appropriate radiological changes, eosinophil granulocytes in the sputum suggest cyst rupture, even in the absence of echinococcus tissue. However, bronchial asthma or Löffler's infiltrates should be excluded clinically. They delayed appearance of peripheral blood eosinophilia after cyst rupture and the development of an eosinophilic broncho-pneumonia is noteworthy.