Clinical assessments of the degree of airway obstruction in asthma are known to be unreliable. Objective measurements of pulmonary function are essential to assessing the severity of asthma. Recently. an inexpensive, portable machine, the Mini-Wright Peak Flow Meter, has become available for clinic and home use. This article describes ways the nurse practitioner can use this meter to improve diagnosis and treatment ofasthma. Peak flow measurements can be used to diagnose asthma, and are especially useful in atypical and severe presentations of the disease. Treatment is enhanced by both clinic and home monitoring of response to medications. Regular home monitoring can also improve patients' abilities to provide self-care. Several examples from a case study are given which illustrate the usefulness of home monitoring in medication management, in detection of diurnal variation ofthe asthma and i n the identification ofacute illness.