Allergic bronchopulmonary aspergillosis (ABPA) may complicate 1% to 2% of all cases of chronic asthma. Twenty-eight patients fulfilling the diagnostic criteria for ABPA but without evidence of proximal bronchiectasis [ABPA-S (seropositive)] were identified over a 12-year period and classified by stage. The majority of patients were in remission but all had chronic asthma. Serum anti-Aspergillus fumigatus (Af) IgG was lower in ABPA-S (n = 28) versus ABPA-CB (central bronchiectasis) (n = 58) at the time of initial presentation (IgG-Af index 3.62 versus 7.80, t = 3.46, P < or = .001). Serum IgG1-Af was significantly lower in ABPA-S as compared with ABPA-CB (t = 2.37, P = .011), as was serum IgG2-Af (t = 1.91, P = .031) and serum IgG4-Af (t = 1.78, P = .041). There were trends toward lower concentrations of total serum IgE, serum anti-Af-IgE, and anti-Af-IgA in ABPA-S. Eleven patients with ABPA-S were evaluated closely for a total of 63 patient-years and only four exacerbations with pulmonary infiltrates were identified. No patient in either group was observed to progress to end-stage or irreversible lung disease when early recognition and treatment were instituted. We conclude that ABPA-S represents the earliest stage or apparently a less aggressive form of ABPA.