Twelve nonsmoking subjects with mild asthma will be selected on the basis of > 18 years of age, a baseline FEV1 of > 60% predicted and a screening PC20 of < 8mg/ml. Subjects will be randomized to perform a methacholine challenge with the Digidoser and the Rosenthal Dosimeter on two different days in an unblinded, crossover manner. The geometric mean PC20 with each dosimeter will be compared with a paired t test. The results of this study will indicate whether the Digidoser has the potential of causing false negative test results or whether the ATS method of determining output should not be used with this dosimeter.