The over-arching goal of this division is to develop a systematic risk assessment approach, to be shared globally, that enables dependable and scientifically rigorous assessment of nanoparticle toxicity. Attention will be paid to setting safe limits to nanoparticles to protect worker and public health. We are establishing toxicological principles and risk assessment models that can be applied widely to varying classes of nanoparticles and nanofibers. Proposed regulations will be science-based and will reflect the physical and chemical properties of nanomaterials. We will integrate not only data from our Harvard NanoCenter but also information generated at other labs, both domestically and internationally. Our methods include not only differing values for physical and chemical properties, but also physiologic-base pharmacokinetic modeling of organ exposure to nanomaterials.