Two cases in which infection of the lung by Helminthosporium was characterized by recurrent attacks of asthma with cough productive of sputum and hemoptysis are presented. Resection of the involved lung in each instance demonstrated bronchiectasis with chronic pneumonia and, in one, multiple abscesses. Many septate hyphae, 2.5 to 3 µ in diameter, were detected in the mucous plugs, bronchiolar mucosa and alveoli. Many colonies of Helminthosporium sp. were isolated from the pulmonary tissues removed aseptically at operation. An analogy is drawn between these two cases and cases of allergic aspergillosis reported in the literature. Most likely the mode of entry is inhalation; study of these two cases suggests infection with Helminthosporium superimposed upon asthma, chronic bronchitis, and bronchiectasis.