To investigate the relationships between allergen inhalation challenge and other diagnostic procedures, inhalation challenge with house dust (HD) allergen, intradermal skin tests with HD allergen, inhalation challenge with methacholine and circulating HD allergen-specific IgE levels were examined in 104 patients with bronchial asthma. Using the single exposure method, allergen inhalation challenge was performed. Forty-three patients had positive bronchial responses to allergen and 61 patients had negative bronchial responses. With serially diluted HD allergen (10-3 to 10-6, w/v), skin-test sensitivity was expressed as the highest dilution required to produce a weal of more than 9.9 mm. With the continuous exposure method, bronchial responsiveness to methacholine was evaluated as the number of units of inhaled methacholine (PD35-Grs) from the start to the point at which Grs had decreased by 35% from its baseline value. The level of circulating HD allergen-specific IgE was measured with the Phadebas. RAST system and the results were assessed as a RAST score. Using discriminate analysis, in which the independent variables were skin-test sensitivity. PD35-Grs and the RAST score, only in 30% of all patients was bronchial responsiveness to inhaled HD allergen predictable. Therefore, we suggest that inhalation challenge with allergen is an essential test for determining the role of a specific allergen in airways at present.