With special emphasis on the paediatric aspects, the importance of peak expiratory flow rate measurements in asthma patients is reviewed. Portable peak flow meters allow for regular home monitoring of lung function. Repeated peak expiratory flow recordings by patients at home are of great value in the diagnosis and the therapeutic management of bronchial asthma. Monitoring of peak expiratory flow rates may improve the perception of compromised airway function and thereby enhance compliance in asthma patients. As a relatively simple form of pulmonary function testing, the measurement of peak expiratory flow rates, however, cannot substitute for pulmonary function testing by spirometry, flow-volume-curves or bodyplethysmography.