Mice were either acutely infected with Aspergillus conidia intranasally or subjected to fungal allergy (ABPA) by repeated sensitization with Aspergillus culture filtrate extracts (5.5±0.7 ng ml−1 versus 11±1.0, total serum IgE in Il9R−/− versus C57BL/6 mice, respectively). The gene discussed is IL9R; the disease is allergic bronchopulmonary aspergillosis.