Thirty cases of allergic bronchopulmonary aspergillosis (ABPA) were treated between 1967 and 1981. Developing in patients with a history of chronic asthma (28 of the 30 cases), the initial manifestations of ABPA developed after long periods (an average of 29 years after the onset of the asthma). Chest radiography demonstrated recurrent labile infiltrates in 28 cases, segmental or lobar atelectasis in 7, and proximal bronchiectasis in 16 cases. A circulating eosinophilia was a constant finding, but this varied with time. Immunologic investigations gave positive skin tests, 19 of the 30 patients only presenting a cutaneous reaction delayed until the 6th hour. Total IgE, determined in 18 cases, varied between 600 and 9400 IU/ml (RIST), with identification of specific IgE for Aspergillus in all cases, though to varying degrees. Serial measurements of total IgE levels showed co-existence of an acute progression of the affection and elevated total IgE in 3 cases, but no correlation was found between serum IgE levels and the severity or chronicity of the disease. Physiopathologic features included immediate and partially delayed hypersensitivity to Aspergillus fumigatus. The frequency of ABPA during the course of mucoviscidosis suggests, by analogy, that a local factor may exist which favorizes Aspergillus fumigatus proliferation in patients with ABPA alone.