It is clear that accurate assessment of the severity of asthma requires a measurement of airway obstruction, such as peak expiratory flow rate. In this study, physicians were quite inaccurate in estimating the peak expiratory flow rate by examining patients, whereas the patients themselves were far more accurate in guessing the measurement. In addition, they were able to tell whether the peak expiratory flow rate was better, the same or worse from day to day. Patients' symptoms are important indices of the severity of airway obstruction which should be exploited in management.