OBJECTIVES: I. Determine whether theophylline will improve the dyspnea rating of patients with cancer who are short of breath and have evidence of respiratory muscle weakness. II. Determine whether this drug will improve the ability to perform daily activities in this group of patients. III. Determine whether this drug will improve objective measures of lung function (e.g., FEV-1, FVC) and maximum inspiratory pressure in these patients. IV. Determine whether the serum theophylline level is related to the magnitude of the effect that is observed in this patient population. V. Determine whether this drug will improve a global rating of quality of life in this patient group.