The temporal association between airway inflammation and airway hyperresponsiveness (AHR) has been analyzed in BALB/c mice sensitized to, and subsequently exposed to, a single intranasal challenge of ovalbumin (OVA). In OVA-sensitized/challenged animals only a small increase in responsiveness to methacholine (MCh) was seen at 8 h, peaked at 24 to 48 h, and resolved by 96 h. An early bronchoalveolar lavage fluid (BALF) neutrophil infiltrate (peaking at 8 h postchallenge; ∼ 72% total cells was observed) that returned to baseline by 48 h. BALF eosinophil numbers did not increase until 48 h ( ∼ 32% of total cells), peaked at 96 h ( ∼ 38% total cells), and remained elevated at 8 d ( ∼ 27% total cells). Airway tissue eosinophilia preceded changes in BALF. Eosinophil peroxidase (EPO) levels in BALF were elevated in OVA-sensitized/challenged mice at 48 h only. BALF TNF- α levels peaked at 8 h, whereas IL-5 and IL-4 levels peaked at 24 h. IL-13 levels were increased at both 24 and 48 h. Mucus-positive cells were not observed in the airway epithelium until 48 h. Administration of IL-5 or VLA-4 antibody prior to OVA challenge prevented the development of AHR in sensitized mice as well as BALF and tissue eosinophilia. These data identify a temporal association between Th2 cytokine production, tissue eosinophil infiltration and activation, and, importantly, both the development and resolution kinetics of AHR. Moreover, the antibody studies further support the association of eosinophilia with the pathogenesis of AHR.