Background: Airway hyperresponsiveness (AHR) to pharmacologic stimuli and sputum eosinophils might be useful in the individual adjustment of long-term asthma management. However, it is not clear whether inhaled glucocorticosteroids (GCSs) provide greater protection against specific surrogate markers of airways inflammation than other means. In addition, detailed longitudinal assessment of changes in airway response with inhaled GCSs has never been carried out. Objectives: We compared changes in AHR to inhaled methacholine and adenosine 5′-monophosphate (AMP) after budesonide treatment in a randomized, double-blind, placebo-controlled, crossover study of patients with mild-to-moderate asthma. Subsequently, we undertook a separate study to examine the time course of the changes in AHR in more detail and the changes in sputum cell counts in relation to budesonide treatment. Methods: In the phase 1 of the study, patients undertook bronchial provocation studies with increasing doubling concentrations of methacholine (0.06 to 16 mg/mL) and AMP (3.125 to 800 mg/mL) before and after budesonide 0.8 mg/daily for 3 weeks. The bronchial responses to the inhaled agonists were expressed as the provocative concentration causing a 20% decline in FEV₁ (PC₂₀). In phase 2 of the study, patients attended the laboratory on 12 separate occasions to investigate changes in PC₂₀ methacholine, PC₂₀ AMP, and sputum cell counts before, during, and after withdrawal of therapy with inhaled budesonide 0.8 mg/daily for 6 weeks. Results: Budesonide treatment for 3 weeks significantly attenuated the constrictor response by 0.8 ± 0.3 doubling doses for methacholine and by 2.6 ± 0.5 doubling doses for AMP. These changes were significantly different from each other (P = .003). Significant variation in PC₂₀ methacholine (P < .05) value, PC₂₀ AMP (P < .001) value, percentage of sputum eosinophils (P < .001), and percentage of sputum epithelial cells (P < .001) were observed throughout the longitudinal assessment of changes in airway response to budesonide. Compared with the other surrogate markers, PC₂₀ AMP appears to be useful in promptly detecting early inflammatory changes of the asthmatic airways; a significant change of 1.6 ± 0.3, 2.2 ± 0.3, and 2.8 ± 0.3 doubling doses of PC₂₀ AMP was observed at 1, 4, and 6 weeks, respectively, in the course of budesonide treatment. Conclusions: The present findings underline the exquisite selectivity of diverse surrogate markers of airway inflammation in response to inhaled budesonide. When compared with that to the other markers, AHR to inhaled AMP is an early and sensitive indicator of the beneficial anti-inflammatory effects of topical GCSs. (J Allergy Clin Immunol 2002;110:855-61.)