The tissue around loose total joint replacement prostheses displays a synovial-like lining comprised of cells that produce IL-1 and PGE2, mediators of inflammation that stimulate bone resorption. Particles of titanium alloy, as well as cobalt-chromium alloy and polyethylene, were found to aggravate the histiocytic response and production of IL-1 and PGE2. Tissue with similar histological and biochemical features was produced in a canine model of the aseptic loose cemented femoral stem.