The production and use of nanoparticles is growing rapidly due to the unique physical and chemical properties associated with their nano-size and large surface area. As the field of nanotechnology vastly expands, many questions involving the effects of nanomaterials on the environment as well as human health have been raised. The objective of this book is to address the growing concern of nanoparticle pulmonary toxicity. Not until the recent increase in utilization of nanoparticles in industry, have the dangers of pulmonary exposure to nanoparticles become a major concern. Analyzes of the dangers of nanoparticle exposures are presently at the forefront of environmental and occupational risk assessment studies. The primary objective of this study is to assess the pulmonary toxicity of ultrafine and fine carbon black and titanium dioxide in vivo on both a mass dose of particle basis as well as on a dose normalized to particle surface area administered. The results of these studies will be utilized to answer the question of whether mass of particles administered or surface area of particles administered is a more accurate dose metric to be employed in pulmonary toxicity studies.