We examined the effects of nitrogen dioxide (NO(2)), ozone (O(3)), particulate matter of <10 microm aerodynamic diameter (PM(10)), and sulfur dioxide (SO(2)) on asthmatics ages 5-34 years enrolled in Medicaid in Cincinnati, Cleveland, and Columbus, OH (N=5416). Our study period was for the summer months, June-August, from July 1, 1991 to June 30, 1996. We preformed Poisson regression analyses for the number of daily emergency department (ED) visits for asthma in each city and on the aggregate data controlling for time trends and minimum temperature. We found a 12% increased likelihood of an asthma ED visit per 50 microg/m(3) increase in PM(10) in Cleveland [95% confidence interval (CI)=0-27%] and a 35% increase per 50 microg/m(3) increase in SO(2) in Cincinnati (95% CI=9-21%). When data were analyzed for all three cities combined, the risk of an ED visit increased for all pollutant increases and specifically by 12% (95% CI=1-23%) per 50 microg/m(3) increase in SO(2). Attributable risk estimates show a five times greater impact on Cleveland over Cincinnati or Columbus. Between 1991 and 1996, air pollutants in Cincinnati, Cleveland, and Columbus increased ED visits for asthmatics enrolled in Medicaid.