Clinical and immunologic characteristics are reported in a series of 20 patients with allergic bronchopulmonary aspergillosis seen by physicians in one consulting service during a period of 9 years. Seventeen of these patients have been identified in the past 2 years, reflecting the increasing recognition of the entity. Fifteen of the 20 patients are believed to have proven diagnoses; the other five are strongly suspected. Asthma, pulmonary infiltrates, and eosinophilia are the usual presenting symptoms. Serum immunoglobulin E was markedly elevated in all patients, and serum immunoglobulin D was normal in four out of five patients sampled. Bronchograms were abnormal in all cases in which they could be done. Lymphocyte transformation may be present in some cases but is not a diagnostic feature. The average age at time of diagnosis was 25.5 years, and seven of the 15 proven patients were 20 or younger.