This study examines the effects of respiratory muscle feedback and breathing retraining (BRT) on lung function in patients with cystic fibrosis (CF). Twenty-six patients with CF were matched for age and severity of disease. Standard respiratory spirometry was performed on all subjects before and after biofeedback training. Thirteen experimental subjects underwent eight sessions of pneumographic or strain-gauge feedback from the abdominal muscles and electromyogram feedback from accessory respiratory muscles to assist in learning diaphragmatic and pursed-lips breathing maneuvers. Control subjects received biofeedback-assisted (hand warming) relaxation training. Results revealed a significant improvement in FEV1 and mean forced expiratory flow during the middle half of forced vital capacity (FVC) for the biofeedback group, while the control group showed no change. A similar trend was noted for FVC. These data suggest that respiratory muscle feedback and BRT may improve lung function in patients with CF.