A prospective controlled trial of home monitoring of peak expiratory flow rate (PEFR) was conducted to determine the usefulness of an objective measure of lung function in association with an education program and a medication self-management plan in reducing morbidity in adult patients with asthma. Thirty-five patients managed themselves, using peak flow readings as the basis for the therapeutic plan coupled with educational intervention, whereas 35 control patients used symptoms and spirometric data for following physicians' treatment plans. After a 6-mo study period, patients in the experimental group showed statistically significant improvements in morbidity parameters (days lost from work, acute asthma attacks, days on antibiotic therapy, physician consultations, and emergency room admissions for asthma), increases in FVC, FEV1, and FEV1/FVC, mean PEFR and mean morning PEFR, decrease in percentage of the mean PEFR amplitude, and a reduction in the use of inhaled beta-agonists, oral theophylline, and oral prednisone. Although improvements in some of these parameters were also found in the control group, they did not reach the levels of significance obtained in the experimental group. The personal use of an objective measure of lung function in association with a medication self-management plan leads to improvement in the patient's condition.