Since the last revision of the national particulate standards, there has been a profusion of epidemiologic research showing associations between particulates and health effects--mortality in particular. Supported by this research, the U.S. Environmental Protection Agency promulgated a national standard for particulate matter [less than/equal to] 2.5 microm in aerodynamic diameter (PM(2.5)). Nevertheless, the San Francisco Bay Area of California may meet this new standard. This study investigates the relationship between daily mortality and air pollution in Santa Clara County (a Bay Area county) using techniques similar to those utilized in earlier epidemiologic studies. Statistically significant associations persist in the early 1990s, when the Bay Area met national air pollution standards for every criteria pollutant. Of the various pollutants, the strongest associations occur with particulates, especially ammonium nitrate and PM(2.5). The continuing presence of associations between mortality and air pollutants calls into question the adequacy of national standards for protecting public health.