Background: With the expiration of the patent on albuterol metered-dose inhalers (MDIs) in 1989, methods to assess in vivo bioequivalence of generic formulations required investigation. Objective: In an effort to develop a sensitive method to document bioequivalence, bronchoprovocation with methacholine chloride was used to assess the dose-response relationship of albuterol as delivered by MDI. Sensitivity was assessed in terms of magnitudes of ED₅₀, the estimated albuterol dose required to achieve 50 % of the fitted maximal value of the pharmacodynamic effect above baseline, and change in response as a function of dose, with emphasis on 1 and 2 actuations. Methods: On separate study days, 15 nonsmokers with mild asthma received randomized nominal albuterol doses of 0 to 576 μg by using specially manufactured MDI canisters. FEV₁ was measured 15 minutes after MDI dosing. Serially increasing doses of methacholine were administered, and FEV₁ was measured after each methacholine dose until a 20 % decrease in FEV₁ (PD₂₀) was achieved. Results: Mean PD₂₀ values after use of each of the albuterol-containing MDIs were significantly greater than either mean screening or mean placebo PD₂₀ values (P <.05). Mean responses and most individual subject responses to 1 and 2 actuations (90 and 180 μg) of albuterol MDI were within the sensitive region of the dose-response curve. The mean estimated ED₅₀ value on the basis of nonlinear mixed effect modeling was 119.2 μg (range, 33.3-337.1 μg), with an intersubject percentage coefficient of variation of 69.0 %. Conclusions: The methacholine bronchoprovocation model is safe and useful in the study of albuterol MDI dose-response in asthmatic subjects. Bronchoprovocation studies may be used for determination of bioequivalence of multisource albuterol MDI products. (J Allergy Clin Immunol 2002;110:713-20.)