Repeated, short-term exposures to ozone (O₃) lead to attenuation of the acute lung function and airway inflammatory responses seen after a single exposure in healthy subjects, but it is unclear whether these acute responses also attenuate in subjects with asthma. To address this question by exposing 14 subjects with asthma to 0.2 ppm O₃ for either 4 hours on a single day or 4 hours on 4 consecutive days (multiday [MD]). At least 3 weeks later, subjects underwent the alternate exposure. Spirometry was performed immediately pre- and postexposure and bronchoalveolar lavage (BAL) was obtained 18 hours after each exposure. The decrease in FEV₁ was greatest across Day 2 of the MD (MD2) exposure and then gradually declined on successive days of the MD exposure (mean ± SD decrease in FEV₁ of 25.4 ± 18.0% across MD2 compared with 4.2 ± 6.5% across MD4). Respiratory symptoms followed a similar pattern to that of FEV₁. Although the concentration of neutrophils in BAL after the MD4 exposure was not significantly different from that after the single-day exposure (1.7 ± 1.3 × 10⁴ cells/ml vs. 1.2 ± 0.8 × 10⁴ cells/ml, p = 0.20), the concentration of alveolar macrophages did significantly increase in BAL after the MD exposure (19.9 ± 9.7 × 10⁴ cells/ml after MD4 vs. 12.1 ± 6.4 × 10⁴ cells/ml after the single day). Alveolar macrophages are recruited to the airways of subjects with asthma with repeated short-term exposures to O₃, suggesting a possible role for these cells in the chronic response to oxidant-induced injury.