Bronchial allergen challenge was performed twice in ten well-defined stable asthmatic patients. On each provocation day the allergen was administered either by a standard method at tidal volume breathing or by a dosimeter method. Ten-fold increasing concentrations of allergen were administered with an interval of 10 min. Total amount of allergen of 9, 90, 900, 9000 and 90000 SQ units using the standard method, whereas the corresponding amount by the dosimeter method was 0.5, 5, 50, 500, and 5000 SQ units. The bronchial response was determined by forced expiratory volume in the first second (FEV1) and by total resistance to breathing (Rt) measured by an opening interrupter method. The provocation was stopped when a decrease of at least 20% of the post-saline FEV1 and a 4O% increase in post-saline Rt, was observed. A PC20-FEV1 and a PC40-Rt was calculated by interpolation on the log dose-response curve. The late reaction was recorded and defined as a 20% reduction in peak expiratory flow (PEF) occurring during the 24-hr period after challenge. The comparability of PC20-FEV1 and PC40-Rt obtained with the standard method and with the dosimeter was high. r= 0.89 and r= 0.88. Furthermore, no significant difference was found by comparing Δ FEV1 and Δ Rt during provocation by either method as well as the occurrence and magnitude of the late reaction. We conclude that there exists a high comparability of the bronchial response to an allergen challenge performed either by a standard method at tidal volume breathing by continuous inhalation of the allergen aerosol or by a dosimeter method of inhalation despite the difference in the total allergen doses inhaled.