The authors compare the methacholine (Mch) and the nebulized ultrasonic distilled water (NUDW) bronchial challenge as regard sensitivity and time required to perform them. For military service fitness, were studied 24 asthmatic patients. Each subject performed random a bronchial challenge by Mch (Yan method) and by NUDW (Allegra method) in two different days; for each bronchial challenge has been measured the time required to perform it. The atopic status has been evaluated by skin-prick test. All the subjects have shown a positive response to Mch test (PD 20 FEV1 mean: 352 mcg, range 80-850) whereas 13 subjects (54%) have shown a positive response to NUDW. The time required to evaluate all the subjects by Mch test has been 199.5 minutes whereas the total time required to evaluate all the subjects by NUDW test (127 minutes) and to evaluate by Mch test the non responders to NUDW (100 minutes) has been 227 minutes. The most of subjects were skin reactors. No difference was found as regard onset of disease, basal lung function and atopic status between responders and non responders to NUDW test. We conclude that NUDW test has shown a lack of sensitivity in this sample (50% of asthmatic patients could be misdiagnosed) and that the Mch test is preferable to determine a rapid method for measurement of bronchial responsiveness.