This proposal relates to the study of problems involved with the long term survival of total hip joint prostheses. Fatigue studies of metallic materials including 316L Stainless steel, cast cobalt chrome alloy, Ti6%A14%V and MP35N are proposed to derive safe allowable stresses with 99% confidence of survival. Wear studies will be continued to study the variables involved in the wear of ultra high molecular weight polyethylene and the mechanisms operative in joint replacement devices. Stress analysis and design studies using finite element techniques for both total hip joint replacement and total knee replacement are proposed. Biocompatibility studies include evaluation of the carcinogenetic potential of implant materials including currently used metallic alloys, ultra high molecular weight polyethylene, Silastic and polymethylmethacrylate. In addition, a bio-assay of the tissue compatibility of RMI titanium alloy is proposed.