A questionnaire was administered to parents of 171 asthmatic children, and their knowledge of asthma was evaluated using a quantitative score. The mean age of children was 5 yr and the mean duration of their asthma was 3 yr. Each sign of the classical triad "noisy breathing, cough, indrawing" was mentioned by two-thirds of parents. Inhaled agents perceived as triggers of asthma were: animal hair (73.7%), dust (69.6%), pollen (60.2%), tobacco (44.4%), molds (14.6%). Other triggering agents mentioned were: stress (51.5%), infections (38%), exercise (13.5%). Mothers with college or university education knew more clinical signs of an attack (P less than 0.01) and more triggering factors (P less than 0.005). Parents satisfied with previous teaching knew more threatening signs of an attack (P less than 0.01). About 80% of those that used theophylline and 49.4% of those that used inhaled beta-2-agonists knew the correct mode of administration. Parents satisfied with previous teaching had better knowledge of the side-effects of theophylline (P less than 0.005) and beta-2-agonists (P less than 0.02). 58.5% of those that used cromolyn sodium did not know the mean duration of a therapeutic trial and 15% did not use it as prophylaxis. 57.1% of those that used oral corticosteroids did not know any side-effects of the drug. About half of the parents indicated that they would like to receive more information about the causes and the appropriate treatment of asthma. It was concluded that parental teaching should focus more on environmental and therapeutic issues.