Dyspnea is influenced by both physiologic and psychologic factors. Breathlessness is common in patients with chronic obstructive pulmonary disease (COPD) and often is the reason that the individual patient seeks medical attention. In order to evaluate the different clinical studies involving the use of theophylline in COPD patients, it is important to consider the three distinct approaches for measuring dyspnea--psychophysical testing, clinical methods, and ratings during exercise. Four randomized, double-blind, placebo-theophylline trials from one to four weeks in duration have evaluated the impact of theophylline on lung function and breathlessness. In these studies, the overall improvement in forced expiratory volume in one second was quite consistent for theophylline compared with placebo therapy. When appropriate clinical methods for measuring dyspnea were used, theophylline showed a positive reduction in breathlessness. These reports suggest that theophylline provides modest objective and subjective improvement in patients with symptomatic chronic air flow obstruction.