This article is a commentary on the following study: Maynard C, Coull BA, Gryparis A, Schwartz J. Mortality risk associated with short-term exposure to traffic particles and sulfates. Environ Health Perspect. 2007;115:751-5. Objective: In a cross-sectional study of approximately 100,000 hospital deaths occurring between 1995 and 2002 in the Boston area (United States), the aim is to test the relationship between daily concentrations of PM10 and sulfates and the risk of mortality using a spatiotemporal regression model. Materials and methods: Health data. Individual mortality data for the period 1995–2002 were obtained from the Massachusetts Department of Public Health. Specific causes of death—cardiovascular disease (CVD), stroke, respiratory diseases, and diabetes—are defined according to ICD-9 and ICD-10. The place of residence at the time of death is geocoded. The analysis covers 107,925 deaths, after excluding deaths for which data on exposure to FNs were missing (March 1997–April 1999), as well as deaths occurring in hospitals, for which it was unlikely that the individual was at home the day before death. (R.A.)