We studied the effect of body weight support on self-selected overground walking speed in both healthy elderly subjects and subjects post-stroke using the KineAssist, a novel robotic gait and balance device. Body weight support is provided by the robot via a closed-loop system that provides support about the subject's estimated center of mass. Body weight support was tested at 10%, 20%, 30% and 40% of the subject's weight. We found that selfselected walking speed decreased with greater levels of body weight support for the healthy elderly subjects. However, the subjects post stroke showed an average increase of 18% in self-selected walking speed at some level of body weight support compared with no body weight support while walking in the KineAssist. Gait speed increases corresponded to an increase in step length. There appears to be a benefit to overground walking speed when providing a small percentage of body weight support for people post-stroke.