Eighteen COPD patients enrolled in a comprehensive, multidisciplinary pulmonary rehabilitation program were randomly assigned to perform either: 1) walking, or 2) ventilatory muscle exercise training (VMT) using a prototype, portable device for isocapnic hyperventilation training. Both groups performed exercise training at home. Twelve patients completed the study and follow-up evaluation (five VMT, seven walkers). Pulmonary function did not change in either group. For the VMT patients, there were modest increases in ventilatory muscle endurance and exercise performance. VO2max and VEmax increased significantly. For the walkers, only walking endurance time increased significantly. These results indicate that isocapnic hyperventilation exercise training can be performed successfully by COPD patients in an unsupervised home setting and can lead to improvement in both ventilatory muscle endurance and exercise performance. Walking exercise training did not improve ventilatory muscle endurance.