Abstract: An exoskeletal robotic device supplements relative movement between biological skeletal members coupled at a biological joint of a wearer, and preferably forms complete sections of a skeleton to be worn by a human. First and second frame members for mechanical joints are attachable to the wearer adjacent the biological joint. The mechanical joints define a center of relative rotation of the frame members about at least two, and preferably three mutually perpendicular axes, the center of relative rotation of the frame members being displaced from the outer surfaces of the skeletal members to correspond in position with the center of the biological joint. Actuation devices in the form of hydraulic cylinders are coupled between the first and second frame members for rotating the frame members under power under control of a microprocessor which can execute stored sequences or apply power in the same direction as exerted by the wearer against pressure sensors coupled to the microprocessor.