ICAM-1 deficiency protects against acute but not chronic airway hyperreactivity induced by viral infection. Wild-type or ICAM-1–null mice were assessed for airway reactivity to inhaled methacholine by measurements of Penh at the indicated times before and after inoculation with SeV (5,000 EID₅₀) or an equivalent amount of SeV-UV. Values are provided for baseline (B) and after exposure to vehicle (V) or methacholine (doubling concentrations, 5–160 mg/ml), and each value represents mean ± SEM of eight to nine mice. Values for Penh in cohorts that were inoculated with vehicle alone were no different from those for SeV-UV treatment (data not shown). *Significant increase from control mice that received SeV-UV. **Significant increase from control mice and from SeV-infected ICAM-1^–/– mice.