The main objective of the present study was to test the hypothesis that patients with cardiopulmonary disease can reliably identify different sensory qualities of their experience of breathlessness. A secondary aim was to examine whether there was any relationship between such specific descriptors of the sensation of breathlessness and a patient's clinical diagnosis. A randomly ordered list of 45 descriptors of breathing discomfort related to exertion was administered on two occasions to 208 patients with cardiopulmonary disease; patients identified the descriptors that applied to their own experience. A total of 169 patients were considered reliable in that their responses were repeatable between questionnaires; there was evidence that an individual's reliability could be assessed by asking repeat questions within a questionnaire. With these patients, individual descriptors generated different degrees of yes and no response and were answered with a variable consistency, suggesting that some questions may be more useful than others in discriminating between the quality of patients' sensations. Overall, patients with obstructive disorders (asthma and chronic obstructive airways disease [COAD]) answered yes more often than those with restrictive or cardiac conditions, possibly reflecting differences in severity of disease. A cluster analysis separated the descriptors into 12 groups which appeared to describe different aspects of breathing discomfort. Relative to their response to other clusters, COAD patients were more inclined to identify distress, asthma patients to indicate wheeziness, restrictive patients to report rapid breathing, and the cardiac group to describe a need to sigh. A second cluster analysis separated patients into 12 groups based on responses for the descriptor clusters. One group contained the largest number of both COAD and asthma patients; another group included the largest number of restrictive and cardiac patients; however, the next largest number for each diagnostic grouping occurred in a different patient grouping. These findings suggest that further development of this approach in defining a patient's breathlessness may, as with pain, provide clinically useful information relating to the etiology and possibly even the treatment of this distressing symptom.