157 healthy new employees of Lausanne University Hospital volunteered for a bronchial provocation test with methacholine. Fifty (32%) reacted with bronchial obstruction. The symptomatic non-smokers without respiratory or allergic history, and without bronchial obstruction at the initial examination, were the least reactive (8 cases in 52), whereas smokers, subjects with a bronchial obstruction and those with a prior history of respiratory or allergic disease reacted more frequently (42 among 105). The most important factor in the setting of the level of bronchial reactivity seems to be the presence of a bronchial obstruction (21 cases among 35).