Future research on particulate matter should focus on which chemical components and other characteristics of these air pollutants are the most hazardous, the National Research Council recommends in a report released on March 24. Particulates are one of the major air pollutants regulated by EPA, and they may consist of dust, soot, sulfur dioxide, or other materials emitted by vehicles, power plants, and forest fires. The NRC report concludes that EPA-sponsored research has led to a better understanding of health problems associated with particulates but says the emphasis of this work should shift. Future research should determine which groups of the population are most susceptible to health effects from particulates, the report says. And there is a need for an understanding of the size and type of particulates being emitted by different sources and for improved computer models to link pollution sources with particulate concentrations in specific areas. In addition, the report, which will be available soon at http://www.nap.edu, recommends a long-term study of the health effects of exposure to particulate matter.