Between 1990 and 1995, 9 French cities provided data on daily air pollution, total mortality, cardiovascular mortality, and respiratory mortality. Personnel in individual cities performed Poisson regressions, controlling for trends in seasons, calendar effects, influenza epidemics, temperature, and humidity, to assess the short-term effects of air pollution. The authors describe results obtained from the quantitative pooling of these local analyses. When no heterogeneity could be detected, a fixed-effect model was used; otherwise, a random-effect model was used. Significant and positive associations were found between total daily deaths in these cities and the 4 air pollution indicators studied: (1) Black Smoke, (2) sulfur dioxide, (3) nitrogen dioxide, and (4) ozone. A 50-microg/m3 increase in Black Smoke (24 hr), sulfur dioxide (24 hr), nitrogen dioxide (24 hr), or ozone (8 hr) was associated with increases in total mortality of 2.9% (95% confidence interval [CI]) = 1.3, 4.4), 3.6% (95% CI = 2.1, 5.2), 3.8% (95% CI = 2.0, 5.5), and 2.7% (95% CI = 1.3, 4.1), respectively. Similar results were obtained for cardiovascular mortality. Except for sulfur dioxide, positive--but not significant--associations were found with respiratory mortality. The internal consistency among the cities studied, as well as consistency with previously published results, favors a causal interpretation of these associations.