A case of allergic bronchopulmonary disease caused by the fungus Penicillium with intermittent airways obstruction, transient pulmonary infiltrate, blood and sputum eosinophilia, positive dual skin tests (type I and III) and precipitating antibodies in the serum is described. An Arthus skin reaction was elicited and supported by histologic and immunofluorescence studies. Bronchial hygiene alone was effective in treatment. The possibility of other airborne fungal spores causing a similar disease is emphasized.