The inspiratory pressure load is an important variable in inspiratory muscle training (IMT), but previous studies with chronic obstructive pulmonary disease (COPD) patients have not controlled for this variable. We compared the effects of two months of IMT with a pressure threshold breathing device at inspiratory pressure loads equal to either 15 or 30% of each patient's maximal inspiratory pressure (Plmax). This study was double blind and patients were randomly assigned to the treatment groups, 12 in the 15% group and ten in the 30% group. Dependent variables were measured at baseline, and after one and two months of IMT. Patients who exercised with the 30% load improved the following: Plmax by a mean of -12 +/- 9 cm H2O (p less than 0.01), endurance time while breathing against an inspiratory pressure load equal to 66% of Plmax by 5 +/- 9 min (p less than 0.01), and 12-min distance walk (12MD) by 199 +/- 90 feet (p less than 0.01). Patients who exercised with the 15% load demonstrated no improvements in Plmax, endurance time, and 12MD. There were no changes in patients' report of functional impairment (Sickness Impact Profile), mood (Profile of Mood States), health status (Health Perceptions Questionnaire), and pulmonary symptoms (respiratory symptom log). We conclude that the 30% load was more effective than the 15% load in this sample.