This article presents findings from updated analyses of data from 90 U.S. cities assembled for the National Morbidity, Mortality, and Air Pollution Study (NMMAPS). The data were analyzed with a generalized additive model (GAM) using the gamfunction in S-Plus (with default convergence criteria previously used and with more stringent criteria) and with a generalized linear model (GLM) with natural cubic splines. With the original method, the estimated effect of PM(10) (particulate matter 10 microm in mass median aerodynamic diameter) on total mortality from nonexternal causes was a 0.41% increase per 10-microg/m(3) increase in PM(10); with the more stringent criteria, the estimate was 0.27%; and with GLM, the effect was 0.21%. The effect of PM(10) on respiratory and cardiovascular mortality combined was greater, but the pattern across models was similar. The findings of the updated analysis with regard to spatial heterogeneity across the 90 cities were unchanged from the original analyses.