In 1986, the U.S. EPA issued an air quality standard for particulate matter that included only particulates below 10 microns in diameter (PM10). Unfortunately, epidemiological research investigating the health effects associated with PM10 has been limited by the lack of available daily data from outdoor monitoring stations. Evidence of high concentrations of PM10 in Eastern Europe and in metropolitan areas such as Mexico City and Santiago, Chile underscores the need to evaluate the association between air pollution and mortality. Over the last few years, daily measures of ambient PM10 have been collected in Santiago. Our analysis examines the relationship between PM10 and daily mortality between 1989 and 1991. In addition to total daily mortality, the data were compiled to record total mortality for all males, all females, and those over 65, and mortality from either respiratory disease or cardiovascular disease. Multiple regression analysis was used to explain mortality, with particular attention to controlling for the influence of season and temperature. The results suggest a strong association between PM10 and all of the alternative measures of mortality. The association persists after controlling for daily minimum temperature and binary variables indicating temperature extremes, the day of the week, the month, and the year. Additional sensitivity analyses suggest a fairly robust relationship. In general, a 10 micrograms/m3 change in daily PM10 was associated with a 1% increase in mortality. This relative risk is consistent with the results of recent studies undertaken in the United States.