There are numerous programs ongoing to evaluate environmental exposure of humans to xenobiotic chemicals (eg: EU ESBIO; US CDC NHANES; Canadian Health Measures Survey). The goal of these projects is to determine relative trends in exposure to chemicals, across time and subpopulations. Due to the lack of data, there is little information correlating biomarker levels with exposure concentrations, and as a result, difficulty in utilizing biomonitoring data for biological guidance values. A suite of model tools would be the most appropriate method to facilitate forwardand reversedosimetry estimations of xenobiotic exposure to aid in interpretation of biomonitoring results. A tiered approach of simple, arithmetic pharmacokinetic (PK) models, as well as more standardized PBPK models, would promote the use of human biomonitoring data in the development of appropriate biomonitoring guidance values (BGVs). The output of these evaluations will be potentially useful in setting hazard/exposure criteria, such as the Derived NoEffect Level values under the EU REACH program. In this project, three types of PK and PBPK models will be developed, utilizing the MEGen model generation application. QSAR estimations of chemical-specific parameters will be included, as well as accommodation of variations in urine production. Estimates of variability in human physiology will also be incorporated, to allow for Monte Carlo analysis of biomarker level concentrations. Validation of each of the model structures will be conducted with published datasets of representative biomarkers. Project sponsored by the Long-range Research Initiative Program of the European Chemical Industry Council (Cefic)