The technical and safety requirements for intracochlear electrical stimulation to restore hearing in the profoundly deaf are reviewed. A system has been implanted in human subjects which comprises a 16-contact flexible electrode array, radio receiver/stimulator and surgical disconnect which permits changing from percutaneous cable to transcutaneous telemetry. The design, fabrication, and mechanical and electrical testing of each of the components are discussed in detail. Major improvements over previous systems include controlled introduction of anisotropic flexing properties in the electrode array to facilitate insertion and optimal contact orientation, enlarged and stabilised contact surface area and the development of a new connector technology which combines high density, high reliability, biocompatibility and ease of operation during surgery.