Controlling drugs and relieving drugs are prescribed for many of the patients and they use their drugs when their symptoms are getting worse. It is still controversial whether that decision should be made on the basis of the patient's perception or PEF. Some studies suggest the significance of peak flow monitoring (PFM), while others are negative about introduction of PEF. Patients tend to underestimate their symptoms, since they cannot evaluate their airway obstruction correctly. It is known that patients without PEF meters are at higher risk of dying from asthma. This review attempts to infer the significance of PEF and PFM especially in the management of adult asthmaticus.