Control of asthma symptoms is, unfortunately, not a reality for many people with asthma. Asthma control is an ongoing challenge, requiring a multidisciplinary treatment approach. The National Asthma Education and Prevention Program (NAEPP) of the National Heart, Lung, and Blood Institute published its Guidelines for the Diagnosis and Management of Asthma in 1997, but the extent of implementation of recommendations in physician's practices remains to be determined. We sought to determine if a systematic implementation of the NAEPP practice guidelines would impact physician's treatment decisions for patients with asthma. The Asthma Care Network is a large, national, point-of-care program developed to assist health care providers in the assessment and management of their patients with asthma. Outcome measurements for the program included level of asthma control, activity limitation, sleep disruption, use of rescue medications, use of controller medications, and urgent care services. A total of 4,901 primary care physicians at 2,876 practice sites enrolled more than 60,000 patients. Nearly three fourths of patients reported symptoms consistent with a lack of asthma control (mean 74%, range 69-81%). Approximately 68% of pediatric patients and 78% of adult patients reported limited activities due to asthma in the past week. Sixty-two percent of pediatric patients and 68% of adult patients reported more than two symptomatic days in the past week. Approximately 40% of the patients surveyed were not using controller therapy. The overall percentage of patients reporting uncontrolled asthma who were prescribed a controller medication increased from 60% to 81%, and the use of inhaled corticosteroids containing medications among these patients increased by 52%. As a result of the assessment of the patients' level of asthma control during the office visit, physicians changed their patterns of prescribing controller therapy in patients with uncontrolled asthma.