Recently, we have shown that allergen-induced airway hyperresponsiveness (AHR) after the early (EAR) and late (LAR) asthmatic reaction in guinea pigs could be reversed acutely by inhalation of the Rho-kinase inhibitor Y-27632. The present study addresses the effects of pretreatment with inhaled Y-27632 on the severity of the allergen-induced EAR and LAR, the development of AHR after these reactions, and airway inflammation. Using permanently instrumented and unrestrained ovalbumin (OA)-sensitized guinea pigs, single OA-challenge-induced EAR and LAR were measured and histamine PC₁₀₀ (provocation concentration causing a 100 % increase in pleural pressure (P_pl))-values were assessed 24h before, and at 6 and 24h after the OA-challenge (after the EAR and LAR, respectively). Thirty min before and 8h after OA-challenge, saline or Y-27632 (5 mM) was nebulized. After the last PC₁₀₀-value, bronchoalveolar lavage (BAL) was performed and the inflammatory cell profile was determined. Inhalation of Y-27632 before allergen challenge markedly reduced the immediate allergen-induced peak rise in P_pl. Also, pretreatment with Y-27632 considerably protected against the development of AHR after the EAR and fully prevented AHR after the LAR. These effects could not be explained by a direct effect of Y-27632 on the histamine responsiveness, because of the short duration of the acute bronchoprotection of Y-27632 (<90 min). Moreover, Y-27632 reduced the number of total inflammatory cells, eosinophils, macrophages and neutrophils recovered from the BAL. Altogether, inhaled Y-27632 protects against acute allergen-induced bronchoconstriction, development of AHR after the EAR and LAR and airway inflammation in an established guinea pig model of allergic asthma.