A motorized forearm module has been developed to operate conventional body-powered prosthetic terminal devices for upper extremity amputees unable to successfully operate these devices themselves. The module attaches between the socket portion of the prosthesis and any string-actuated terminal device, replacing the foam forearm section generally used as a spacer. Operation is either by switch or myoelectric control, and is suitable for those individuals who prefer the functionality of a conventional terminal device but do not have the necessary strength or shoulder excursion to use one. An overall description of the module is given and the results of the initial clinical trials are reported.