Background: The methacholine challenge test is commonly used to evaluate bronchial responsiveness in diagnosis and follow-up of asthmatic patients. Objective: To investigate late effects of methacholine challenge on induced sputum. Methods: Ten non-smoker patients with mild or moderate stable asthma were recruited. At 12:00 p.m., patients were randomly assigned to inhale either methacholine (challenge) or physiologic saline. At 6:00 p.m., sputum induction was performed. On the second visit, one week apart, patients completed their participation in the study by undergoing another inhalation and sputum induction. Results: After methacholine, 8.6 ± 9 g of sputum were expectorated with 8.6 ± 6 million cells, 78 ± 10% were viable, and 6.8 ± 7% eosinophils. These data were not different from results obtained after saline: sputum amount = 7.6 ± 6 g, total cell count = 12.4 ± 12 million, viability = 82 ± 10%, and eosinophils = 6.6 ± 9%. Expiratory flow (PF) peak fall during sputum induction was not different: 21.4 ± 12% after methacholine and 18.4 ± 15% after saline. The PF fall observed during induction correlated with the amount of expectorated sputum (p = 0.018) and eosinophil relative number (p = 0.003). No other significant correlation between lung function measurements and sputum characteristics was found. Conclusion: A methacholine challenge carried out six hours before sputum induction does not significantly alter the cellular constituents or amount of sputum.

Keywords: Asthma. Methacholine chloride. Bronchial provocation tests.