In almost any workplace in which one might study the effects of low-level ionizing radiation, there are chemical exposures that are integral to the process and to which many works can be simultaneously exposed. This can lead to the problem, well recognized in epidemiology, known as confounding. In order to confound the radiation dose-response relationship, the exposure must be associated both with exposure to radiation and with the health effect being studied. It is important to account for this confounding since it can influence or bais the conclusions of the study. Not doing this can lead to spurious findings of associations of a health effect with the agent under study, or worse, result in not finding an association where in truth there is one. HERB scientists have conducted, and currently are conducting, studies in which a number of chemical exposures are present and are being assessed along with the radiation dose. For example, in a study of the relationship between external ionizing radiation and lung cancer at a nuclear naval shipyard, historical worker exposures to asbestos and welding fumes are being reconstructed. This is being done since it is likely that such industrial hygiene exposures are associated with radiation exposures and with lung cancer. Similarly, a study of the relationship between internal dose from plutonium deposition and lung cancer at Rocky Flats assessed the potential confounding effects of a number of chemical agents, including asbestos and carbon tetrachloride. In conducting such studies, historical industrial hygiene data are typically sporadic, are limited in quantity and quality, and often are problematic in reconstructing exposures. A variety of creative exposure assessment techniques have been used to quantitatively or qualitatively estimate historical exposures in studies of the adverse health effects of ionizing radiation, and these will be presented and discussed.