This report, Data Sources Available for Modeling Environmental Exposures in Older Adults, focuses on information sources and data available for modeling environmental exposures in the older U.S. population, defined here to be people 60 years and older, with an emphasis on those aged greater than 65. The information was gathered as part of the U.S. Environmental Protection Agencys (EPAs) Aging Initiative project. In general, this report contains the same type of information found in EPAs Exposure Factors Handbook (e.g., NCEA, 1997a,b) but with older adults as the sole population subgroup of interest. We envision that this report will be used to inform exposure assessors about the data available for modeling exposures to older people. In addition, the data enable scientists to check or evaluate results obtained from the modeling assessments for older adults, such as determining whether the distribution of ventilation (breathing) rates seen in a particulate matter (PM) intake dose rate assessment, for example, is realistic or not. The same is true for their time spent in motor vehicles, outdoors, or indoors. Intra- and interindividual variability measures are discussed for all of these parameters, where available. In the situation where a time-averaged exposure model is used, the data in this report can provide aggregate information on many of the inputs needed for that type of model. This report can be a useful source book on older adult exposure modeling, similar to the Exposure Factors Handbook. The report is centered on the inputs needed for two of EPAs inhalation exposure models, the Air Pollution Exposure (APEX) model and the Stochastic Human Exposure and Dose Simulation (SHEDS) model. The report also includes a review of physical activity data available for evaluating model outputs. In addition, the report includes discussion of how general health status of older adults might affect exposure to environmental contaminants and an assessment of the interactions between exposure and possible impacts of older people on environmental loadings. The latter category focuses on pharmaceutical discharges into bodies of water. The appendix provides information on developing conditional probabilities for those individuals that have both arthritis and one or more co-morbidities often associated with it. Data shortcomings and research needs are described for each topic covered. Finally, this report presents detailed information on changes in time use, activity, and physiology as people age. It is important to understand these changes because older adults are becoming a larger proportion of the total U.S. population, and more and more societal resources will be directed toward their maintenance.