The traditional approach of caring for patients with chronic respiratory disease has been to rely on pulmonary function tests to quantify the severity and to assess response to therapy. However, patients with respiratory conditions seek medical attention because of symptoms, particularly dyspnea, and impaired ability to function, which clearly impact on an individual's health-related quality of life (HRQOL). Accordingly, instruments have been developed to provide a standardized method to measure health status and levels of impairment. One of the major reasons for measuring HRQOL is to detect how much HRQOL has changed in response to therapy (an evaluative instrument). A minimum clinically significant change has been established for some HRQOL instruments in order to indicate the relative value of any measured change and to guide the interpretation as to whether the change is "clinically meaningful." Selected studies using disease-specific instruments have demonstrated that beta(2)-agonist, anticholinergic, and theophylline medications can improve HRQOL, as compared with placebo therapy.