Because many environmental toxicants are ubiquitous, humans are continuously exposed to them. At other times, certain populations may be more highly exposed to these toxicants from point sources. The evaluation of the degree of the exposure to either a population or an individual is frequently based on indirect surrogates of exposure, such as questionnaire data on time-activities and/or concentrations measured in environmental media. We prefer to assess the degree of the exposure to a given toxicant by measuring the concentration of the toxicant, its metabolite(s), or reaction product(s) in human specimens. Then by applying pharmacokinetic information for that toxicant, we can best reconstruct the exposure scenario. These data are then compared to reference range levels of these toxicants in the preferred biologic specimen. The development and uses of the reference range data are exemplified by case studies including potential exposure to dioxin and solvents.