Recent studies have associated particulate air pollution with daily mortality in a number of U.S. communities. This study sought to replicate those analyses in Cincinnati, Ohio, and to test the strength of the association to the deletion of days with extreme weather conditions and to sensitivity analyses in the analytical approach. This study demonstrates the use of graphical diagnostic procedures to assure adequate control for season and weather and to confirm that the risk is particularly elevated in the elderly and for deaths from pneumonia and cardiovascular disease. Daily total suspended particulate (TSP) concentrations were available in Cincinnati from 1977 to 1982. They were matched to daily counts of nonaccidental deaths, temperature, and dew point temperature. Poisson regression analysis controlled for seasonal and monthly variations and potentially nonlinear relationships to temperature and humidity. TSP was associated with increased risk of mortality. The relative risk for a 100 micrograms/m3 increase in TSP was 1.06 (95% CI = 1.03-1.10). The relative risk for the elderly was higher (1.09), as was the risk for pneumonia (1.18) and cardiovascular disease (1.08). The similarity to recently reported results in Philadelphia is striking. Given the consistent findings from multiple locations, the relationship should be considered causal.