Polycyclic aromatic hydrocarbons (PAHs), which consist of two or more fused aromatic rings, are ubiquitous products of combustion. These compounds are found in wood and tobacco smoke, engine (particularly diesel) exhausts, and in numerous workplaces, including those producing coke and aluminum and those processing hot asphalt. Because some PAHs are potent carcinogens, it is important to assess the levels of exposure to these compounds that are received by workers and the general public. However, PAHs are difficult to measure in the environment because they exist in both the gas phase and the particulate phase, and the carcinogenic particle-bound compounds are present at very low concentrations. In contrast, the smaller vapor-phase PAHs are more abundant in the environment and produce a host of urinary products that can be used as biomarkers of exposure. Here we consider the hypothesis that urinary biomarkers of naphthalene (a 2-ring compound) and phenanthrene (a 3-ring compound) can be used as measures of exposure to total PAHs. We test this hypothesis in three distinct phases of research. First, we determine the predictive value of airborne naphthalene and phenanthrene as measures of exposure to diesel exhaust in a controlled chamber study. Second, we determine the predictive value of urinary levels of naphthalene and phenanthrene as measures of occupational exposure to diesel exhaust, asphalt emissions, and coke-oven emissions. And finally, we develop statistical models of urinary biomarkers of naphthalene and phenanthrene in asphalt-exposed workers to determine effects of particulate PAH levels in air and on the skin, job categories and tasks, and physiological factors that might affect the uptake and elimination of these compounds. Overall, this research demonstrates that urinary biomarkers of naphthalene and phenanthrene can be used as measures of exposure to total PAHs in air and on the skin.