A careful medical history, a physical examination, and tests of lung function provide the information needed to diagnose asthma. Measurement of lung function is useful both for diagnosis of asthma and to monitor the course of the disease. Such tests include spirometry, which provides an assessment of airflow limitation, and peak flow, which measures the maximum speed at which air can flow out of the lungs. Spirometry is performed in a health care professional's office, while peak flow can be tested with portable, plastic peak flow meters ideal for use in home and work settings. Peak flow monitoring provides most patients, together with their health care providers, an effective method to monitor their disease and evaluate their response to therapy.