Forty-two corticosteroid-dependent asthmatics were studied to determine whether their underlying disease might be allergic bronchopulmonary aspergillosis (ABPA). The clinical and laboratory characteristics studied included age, sex, atopic status, mean corticosteroid doses, skin tests to Aspergillus fumigatus (Af), precipitins to Af, total serum IgE, and chest roentgenograms. Twelve patients had four or more of the seven primary criteria used and were considered as the ABPA suspect group. Further studies identified three patients who were considered to have definite ABPA and an additional three patients with probable ABPA. This study suggests that previously undiagnosed ABPA can be detected in populations of corticosteroid dependent asthmatics. Corticosteroid therapy may mask ABPA, and serial evaluations of these patients may be of value in detecting additional cases of the disease.