Continuous methacholine inhalation with simultaneous bronchial resistance monitoring was performed in 15 controls and 26 asthmatic patients. The subjects were in quiet tidal breathing, and the airway resistance measured by forced oscillation method were continuously recorded with X-Y recorder. The mean airway resistance of the asthmatic patients was higher than that of the control group, so was the conductance of the asthmatics lower than that of the control. All the asthmatics were responsive to the methacholine test, while only two controls had the response. No correlation could be obtained between bronchial reactivity and sensitivity, but the bronchial sensitivity was correlated with serum total IgE (r = 0.448; p less than 0.05), and suggest that the higher the IgE is, the more sensitive the asthmatic patients respond to methacholine. Continuous methacholine provocation is useful in the diagnosis of bronchial asthma and is more safe and time-saving compared with conventional intermittent method.