Electromyography (EMG) of diaphragm (Edi) and intercostal muscle (Ein) in 30 healthy volunteers and 28 patients with cor pulmonale or pulmonary fibrosis were analysed. The results show that (1) there is no obvious activity of Ein to be observed and the frequency spectra are stable when the healthy volunteers breath quietly, (2) the activity of Ein and the amplitude of Edi increase when patients are in compensation stage, (3) the patients with serious respiratory failure, the amplitude of Edi decreases remarkably, (4) the frequency spectras of Edi appear wave-like changes with the breathing pattern of patients.