In recent years, regulations regarding snowmobile recreation in Yellowstone National Park have become more restrictive. New regulations limit the number of snowmobiles entering the park, restrict the engine type, and require that all riders must utilize a licensed guide. Given these regulations, it is hypothesized that occupational exposures to the combustion products from snowmobile exhaust have decreased. This research project performed occupational exposure monitoring of National Park Service Employees while working at the West Entrance to Yellowstone National Park during the 2004-2005 winter season. Products of snowmobile exhaust including carbon monoxide, nitrous oxides, volatile organic compounds, fine particulates, and noise were sampled and the analytical results compared to the occupational exposures during previous years. The purpose of this research is to determine if compliance with current regulations regarding snowmobile recreation in Yellowstone National Park has any affect on the occupational exposures received by park employees during the performance of their normal job tasks.