Rationale: Platelets are essential for pulmonary leukocyte recruitment, airways hyper-responsiveness and bronchial remodeling in animals with allergic inflammation and can be found in broncho-alveolar lavage of sensitized animals. No studies however, have explored the direct migration of platelets to lungs. Objectives: To assess whether platelets migrate into lung parenchyma in response to inhaled allergen in ovalbumin-sensitized mice; to assess the role of the FcRI receptor in this phenomenon and to evaluate whether platelets from asthmatics, or from sensitized mice, undergo chemotaxis in vitro in response to relevant antigens. Methods: Ovalbumin-sensitized wild-type mice, or FcR^-/- mice lacking the FcRI, were challenged with aerosolized allergen and lungs analyzed by platelet-specific immuno-histochemistry. In some experiments, mice were depleted of platelets and cross transfused with either wild-type or FcR^-/- platelets to assess the role of platelet FcR^-/-. Chemotaxis of platelets from asthmatics or from sensitized mice was studied in vitro. Main Results: Histology of lungs revealed isolated platelets, migrating out of vessels and localizing underneath the airways after allergen challenge in wild-type, but not in FcR^-/- mice. Platelets from asthmatics and from sensitized wild-type mice, but not from sensitized FcR^-/- mice, migrated in vitro towards the relevant allergen or an anti-IgE. Platelets from normal mice were found to express FcRI and platelet-bound IgEs were increased in sensitized mice. Conclusions: Platelets migrate extra-vascularly in response to a sensitizing allergen via a mechanism dependent on the interaction between allergen, allergen-specific IgE and the FcRI and this may allow them to participate directly in allergic tissue inflammation.