Measurement of lung function is essential for diagnosing and assessing the severity of asthma. This survey showed that lung function tests are rarely used inthe management of asthma in Thailand, which maylead to underestimation of asthma severity.According to the asthma management guidelines,peak expiratory flow monitoring is essential in theassessment of asthma severity. The variability of peakflow meter readings provides a reasonable index ofasthma severity, but only 13.4% of patients surveyedhad ever heard of a peak flow meter, and only 3.2% ofpatients had a peak flow meter at home. Severity classification using day-time and night-time symptomscorrelates with hospital admissions due to asthma.Thus, the need for peak flow meter readings in theassessment of asthma severity could be disputed.However, their role in patient self-monitoring ofasthma deterioration is important and their wider usefor this purpose should be encouraged