The energy required to walk using a newly designed knee-ankle-foot orthosis (KAFO). has been evaluated. The new KAFO locks the knee during stance and allows free-knee motion during the swing phase of gait.The energy required for gait on level ground and on a slope with a 5-percent incline was evaluated inapostpolio subject. Comparisons were made between the standard locked-knee KAFO and the free-knee (unlocked) configuration. The oxygen consumption rate (ml/kg/ min) and energy cost (ml/kg/m) were significantly lower during free-knee gait. The results of the study show that a KAFO design that allows free-knee motion during swing is effective in lowering the energy required for walking.