Five stages of allergic bronchopulmonary aspergillosis were identified in 40 patients studied for several years. The stages are acute, remission, exacerbation, corticosteroid-dependent asthma, and fibrotic. The acute stage has all criteria of the disease and responds to prednisone. The remission stage is free from significant asthma or exacerbations. The exacerbation stage has recurrent flares of acute allergic bronchopulmonary aspergillosis. The corticosteroid-dependent asthma stage may have recurrent exacerbations of allergic bronchopulmonary aspergillosis and severe asthma. The fibrotic stage is an advanced stage of radiographic abnormalities with asthma, irreversible and partially reversible obstructive pulmonary function changes, and poor prognosis. Measurement of IgE and IgG antibodies against Aspergillus fumigatus is of diagnostic value in all stages.