Patient knowledge of asthma and treatment and compliance levels were assessed among 100 moderate to severe asthmatics recruited from general practice. With the use of postal questionnaires non-compliance was found to be high: 39% of patients omitted to take their asthma treatment as prescribed. The level of patient knowledge had no significant effect on compliance to drug therapy. The highest compliers were respondents who reported never receiving an explanation about the condition. The majority of patients believe they would know how to manage an attack, but when they 'scored' on their ability only 34.4% were deemed to be safe. However, the level of patient knowledge appears to influence a patient's ability to manage an asthma attack. Less than half of the patients who had had asthma explained to them reported to have understood the initial explanation, and explanations made by nurses were particularly poorly understood. The study identifies reasons why patients do not comply with drug treatments. Many feel the drugs are not necessary and many forget to take them. Almost half of the cohort admit a reluctance to use their inhalers in public and a third state a preference for tablets rather than inhalers. Health professionals must look at other means of improving patient compliance rather than education in isolation. Since the general practitioner contract was introduced in April 1990, nurses working in general practice have become increasingly involved with health education as part of health promotion and chronic disease management clinics. This study highlights the need for further education in this area.