Stroke is one of the most common diseases that afflict the elderly worldwide. Often people who have suffered a stroke lose the ability to walk. A long and intensive rehabilitation process is needed to recover basic gait functions. Current training is labor intensive and thus expensive. These costs make robotic aids an interesting alternative. To this end we are developing an exoskeleton , LOPES , for the rehabilitation of stroke patients. Our approach to this problem is based on achieving active participation from the patients side supporting only those areas that need to be supported. A novel series elastic type actuator driven by bowden cables was designed for low-weight high performance for this exoskeleton. Current results indicate that the robot allows free motion with little change in EMG compared to walking without the exoskeleton.Clinical test should start in the first half of 2007.