Methacholine challenge test (MCT) is a diagnostic test to assess airway hyperresponsiveness, one feature of asthma. Our study presents the results of MCT, done in our pulmonary function laboratory, correlated with patients' symptoms and allergic status. This is a cross-sectional study, where 134 patients were included : 60 patients had a PC-20 < or = 32 mg/ml (MCT+ group), while 74 had a PC-20 > 32 mg/ml (MCT- group). Dyspnea and wheezing were correlated to positive methacholine reactivity while cough was inversely correlated to it. In the 66 patients presenting isolated cough, 21 were MCT+ (32%). Methacholine reactivity was correlated to positive prick test, particularly for dust mite allergy (p = 0.006). There was a positive trend towards a higher incidence of dyspnea and wheezing with lower methacholine concentrations (p < 0.01), and lower incidence of cough with lower methacholine concentrations (p = 0.004). MCT was valuable in excluding the diagnosis of asthma in more than 50% of the cases and when positive, a good tool in guiding therapeutic choices. It showed a high correlation with the atopic status of the patient. It has definitely its place in diagnostic approach of respiratory symptoms.