The relation between air pollution and mortality in London was examined for the winters of 1958-1972. The data exhibited a high degree of autocorrelation, requiring analyses using autoregressive models. There was a highly significant relation between mortality and either particulate matter or sulfur dioxide (after controlling for temperature and humidity), both overall and in each individual year. Graphic analysis revealed a nonlinear relation with no threshold, and a steeper exposure-response curve at lower air pollution levels. In models with both pollutants, particulate matter remained a significant predictor with about a 10% reduction in its estimated coefficients, while sulfur dioxide was insignificant, with a large drop in its estimated coefficient. The authors conclude that particulates are strongly associated with mortality rates in London, and the relation is likely causal.