In this study, the authors assessed the relationship between air pollution and daily mortality from June 2000 to December 2001 in Shanghai, the largest city in China. They used the generalized additive model to allow for the highly flexible long-term and seasonable trends, and for nonlinear weather variables. In the single-pollutant models, the authors found significant associations between concentrations of air pollutants (particulate matter less than 10 microm in aerodynamic diameter [PM10], sulfur dioxide [SO2], and nitrogen dioxide [NO2]) and daily mortality. An increase of 10 microg/m3 in PM10, SO2, and NO2 corresponded to a respective increase in relative risk of mortality from all causes of 1.003 (95% confidence interval [CI] = 1.001, 1.005), 1.014 (95% CI = 1.008, 1.020), and 1.015 (95% CI = 1.008, 1.022). In the multiple-pollutant models, the association between SO2 and daily mortality was not affected by the inclusion of other pollutants; for PM10 and NO2, however, the inclusion of other pollutants possibly weakened the effects between these 2 pollutants and mortality. This finding suggests that gaseous pollutants may be more important than particulate matter as indicators of health in Shanghai. The authors' analyses provided evidence that the current amounts of air pollution in Shanghai continue to adversely affect population health, and strengthen the rationale for limiting the quantities of pollutants in outdoor air.