Metallic orthopaedic implants have a long history of safety and effectiveness when used for the appropriate indications and when implanted properly. It is recognized, however, that in the long term, these implants may be associated with adverse local and remote tissue responses in some individuals. These adverse effects are mediated by the degradation products of these implant materials. Much of the interest in the long term effects of implant materials has centered on the metallic components because of their tendency to undergo electrochemical corrosion resulting in the formation of chemically active degradation products. Concern about the release and distribution of metallic degradation products is due to the known potential toxicities of the elements used in modern orthopedic implant alloys - particularly cobalt and chromium. Metal toxicity may be mediated by (i) metabolic alterations, (ii) alterations in host/parasite interactions, (iii) immunologic interactions of metal moieties by virtue of their ability to act as haptens (specific immunological activation), anti-chemotactic agents (non-specific immunological suppression), or lymphocyte toxins, and (iv) by chemical carcinogenesis. The potential local and systemic implications of the release and accumulation of metal degradation products from orthopaedic implants will be reviewed.