In the proposed rule on the National Ambient Air Quality Standards for particulate matter (PM), Environmental Protection Agency (EPA) committed to conduct a review and assessment of the numerous studies relevant to assessing the health effects of PM that were published too recently to be included in the 2004 PM Air Quality Criteria Document (AQCD). This report presents the findings of EPA's survey and provisional assessment of such studies. EPA has screened and surveyed the recent literature and developed a provisional assessment that places those studies of potentially greatest relevance in the context of the findings of the 2004 PM AQCD. The focus is on: (a) epidemiologic studies that used PM2.5 or PM10-2.5 and were conducted in the U.S. or Canada, and (b) toxicology or epidemiologic studies that compared effects of PM from different sources, PM components, or size fractions. Given the limited time available, the provisional assessment presented here does not attempt to critically review individual studies or to provide the kind of full integration found in a typical AQCD.