Differences between patients' knowledge and behavior in relation to asthma may account for continuing morbidity in theface of professional and public asthma education campaigns. We conducted a qualitative study of beliefs that support asthma-related behavior, obtaining data from interviews with 70 adult patients. Analysis identified four clear subgroups, or "streams," of adults with asthma: an "anonymous" stream, who doubt that they have asthma and manage symptoms outside the organized health system; an "isolated" stream, who feel dependent on bronchodilators and do not understand the potential of preventive therapy; a "suboptimal" stream, who are confident that they are managing their asthma effectively but who are excessively reliant on bronchodilators; and an "optimal stream," who have high expectations of outcomes and participate actively in a partnership with a doctor. Characteristics of the doctor and the doctor-patient relationship are important elements in altering asthma-related behavior in ways that may facilitate the best health outcomes.