We studied the short-term effects of Paris winter air pollution (i.e., sulfur dioxide, Black Smoke, suspended particulates with an aerodynamic diameter close to 10 microm, and nitrogen dioxide) in 40 nonsmoking mild to moderate asthmatics (52% male; mean age = 46 y; 90% treated with inhaled steroids). During a 6-mo period, subjects recorded asthma symptoms and three daily peak expiratory flow measurements. Statistical analysis (i.e., generalized estimating equation models that accounted for autocorrelation of responses, weather data, and time trends) revealed consistent and significant associations between the pollutants and asthma attacks and symptoms in the entire study group, especially in the subgroup of individuals who took inhaled beta2 agonists as needed. Pollutants correlated negatively with morning peak expiratory flow in the subgroup that took inhaled beta2 agonists as needed, and they correlated positively with daily variability in asthmatics who received regularly scheduled inhaled beta2 agonists. The effects lingered several days after exposure occurred. Low-level pollution has consistent measurable effects on nonsmoking adults who have well-treated mild or moderate asthma.