There are various methods for gait exercise in rehabilitation medicine. These methods are useful for patients to control weight bearing and gait pattern. But they have good points and bad points. The purpose of this study was to determine the effects of weight release on cardiopulmonary function during walking, and to examine the potential of this weight-release method in rehabilitation medicine. Subjects were 15 males who had no cardiopulmonary disease or past illness. They wore a respiratory mask connected with metabolic analyzers and a lifting jacket, and they performed three walking tasks on a treadmill at 4.8 km/hour speed for five minutes. During walking, they were lifted up for the weight release employing 3 different traction forces, by a lifting system (Pneu-Weight, Pneumex, Inc.). The three conditions for traction were adjusted for their body weight percentage : 0% (full weight bearing ; FWB), 25% and 50% body-weight release. Each trial was measured with a metabolic analyzing system and electromyography. There were no significant differences among the three conditions in respiratory parameters such as oxygen uptake and minute ventilation. However, systolic blood pressure significantly decreased in the FWB condition. There were various sorts of changes in the integral electromyogram. For example, gastrocnemius increased and decreased, bicepsbrachii increased without weight-releasing, and increased more with weight-release. During exercise, oxygen uptake corresponded to the amount of muscle activity, and ventilation and heart rate were increased by oxygen requirement increases. These results indicate that weight-release saved muscle activity, and gait patterns were changed to less thrust force. The amount of total muscle activity as a postural adjustment and thrust was unchanged in this gait, but muscles used were altered. In rehabilitation medicine, we should give much thought to these changes. This weight-release walking method is useful, because the load can be adjusted according to the breathing circulation constant.