Abstract Nanomaterials are of interest in many biomedical applications for potential enhancements in structural strength of bone implants, controlled drug release, improved chemical interactions, and scaffolding for cell in-growth and tissue replacement. Unfortunately, the key changes in material properties that enhance performance seem to lead in some cases to increased toxicity. By shifting the distribution of wear particle sizes to smaller individual particles, adverse effects may be created, either directly from the nanoparticle interactions or through intermediary species, such as reactive oxygen. Either way, biological activity often seems to be dependent on particle size, and deleterious side effects and workplace hazards must be evaluated and avoided.