Molecular epidemiologic research involves the identification of relations between previous exposure to some putative causative agent and subsequent biological effects in a cluster of individuals in populations. There is intensive current research in the field of molecular epidemiology, and this research has a direct impact on risk assessment processes. Many of the challenges facing risk assessors today can be addressed by research focused on developing a better understanding of (a) exposure characteristics or assessment, (b) the relationship between exposure and dose, and (c) the ultimate exposure/dose effect response relationship. Results from this research can be used to design and implement preventive interventions in at risk populations. Thus, the application of research in exposure assessment and molecular epidemiology to risk assessment and preventive interventions makes this a core program for public health.