The Phase II project is to complete development of a new Rolling Joint Prosthetic Leg comprising a Rolling Joint (Free-Flow) Foot and Ankle and the Rolling Joint Prosthetic Knee. Original design of both prostheses is based on a Rolling Joint Technology, recently developed by the applicants. The Rolling Joint Foot and Ankle was commercialized in October of 1999. Major efforts during the Phase I of the current study were developed to design, manufacture and testing of the new Rolling Joint Knee. As results of the Phase I study showed, development of Rolling Joint Prosthetic Leg has merit to be continued. Development and testing of the Rolling Joint Knee will be completed during the Phase II proposed. Additional research will be conducted to verify the hypothesis that patients with trans-femoral amputations will benefit from aan assembly of both Rolling Joint Units in a Rolling Joint Leg. New methodology for individual tuning of critical parameters of prostheses will be developed. It will provide more normal, less painful locomotion in a lower limb amputee and increase number of patients to be managed prosthetically. The specific aims of the Phase II project. Complete a development of a new Knee unit prototype with compliant tibial component; conduct a comparative mechanical tests and biomechanical gait study with 20 trans-femoral amputees to verify the hypothesis that a new prosthetic device with the proposed mechanical outcome improves a trans-femoral amputee gait by normalizing "stump-socket" interface during stance phase of gait. Long term objectives of the proposed research are to develop a functional, reliable and economical prosthetic modular system. PROPOSED COMMERCIAL APPLICATIONS: Potential commercial application is the creation of a product line of Rolling Joint Feet and Knees. The RJ Leg will enhance performance of transfemoral amputees without increasing the cost, thus providing a highly competitive product in the field of prosthetic rehabilitation.