Platelet P-selectin is required for pulmonary eosinophil and lymphocyte recruitment in allergen-sensitized mice previously depleted of platelets. Sham- and OVA-sensitized mice were exposed to allergen, and BAL fluid was obtained 24 hours after the third day of challenge and analyzed for eosinophil and lymphocyte numbers. In some groups, mice were rendered thrombocytopenic with the administration of busulfan. Selected groups of thrombocytopenic mice were administered (A,C) washed platelets from P-selectin–deficient (P-sel^-/-WP) or normal mice (WTWP) or (B,D) stimulated platelets coincubated with a P-selectin blocking antibody (FSP + αP-sel) or control IgG (FSP + IgG). n = 3-4 animals per group. Data are expressed as mean ± SEM. ^*P < .05; ^**P < .01.