The National Center for Environmental Health’s Health Studies Branch (HSB) at the Centers for Disease Control and Prevention (CDC) is the response branch for the Center. HSB conducts rapid epidemiologic investigations in response to outbreaks that are believed to have environmental causes and responds to natural and technologic disasters. HSB also conducts extended research studies to more accurately define the relation between human health and environmental exposures. When requested, HSB provides technical assistance and expertise to state or local public health agencies that evaluate the health of populations and the environment in which they live. Recommendations based on the results of HSB’s work have been incorporated into public health strategies to prevent or reduce harmful environmental exposures.