We studied eight men with chronic obstructive pulmonary disease (COPD) (age, 60.57 +/- 7.59 years; height, 162 +/- 10.43 cm; weight, 65 +/- 9.7 kg). Functional values of the sample were as follows: FEV1, 46 percent; FVC, 67 percent; PO2, 72.4 mm Hg; and pH, 7.41. We used a modification of the Nickerson and Keens method. Patients were required to perform 65 percent of maximal inspiratory pressure (MIP). We counted the time from the start of the test to exhaustion of the patient (TLIM). We measured basal MIP and maximal expiratory pressure (MEP) (TLC) at the TLIM and 10, 20, and 30 minutes and MIP was different from the basal value (MIP basal, 85.7 cm H2O; MIP 10 minutes, 79.1 cm H2O; MIP 20 minutes, 78.6 cm H2O; MIP 30 minutes, 79.6 cm H2O. The MEP was not different from the basal value. We concluded that in patients with COPD, MIP decreases significantly after inspiration through umbral inspiratory weight equal to 65 percent MIP and does not return to basal value for 30 minutes. The MEP does not change with respect to basal determination.