The chronic inflammation in asthma evolves by cells including eosinophils, mast cells and lymphocytes. Despite their principal function in hemostasis, platelets contribute to pathogenesis of asthma that activation of platelets occurs following antigen provocation and during asthma attack Our aim was to evaluate the platelet functions and other hemostatic features of children with asthma, both during symptom-free period and asthma attack We enrolled patients with asthma attack (n = 33), mild intermittent asthma (n= 18), mild persistent asthma (n = 15) and healthy children (n = 20). Demographic characteristics and disease-related features were noted. Platelet aggregation and secretion tests (expressed as ATP release) were performed by lumiaggregometer method by stimulation with collagen, epinephrine, ADP, thrombin, ristocetin and arachidonic acid. Plasma levels of D-dimer, factor VIII (FVIII) and von Willebrand factor (vWF) were assessed. There were no differences in platelet aggregation induced by agonists between study groups. ATP release from platelets of patients with asthma exacerbation induced by ADP was lower compared with mild intermittent asthma (P<0.001). Epinephrine-stimulated ATP secretion was also lower in patients with asthma attack than mild intermittent (P=0.039) and mild persistent asthma (P=0.011) and controls (P= 0.018). vWF measurements were higher in children with asthma attack than other study groups (P= 0.001). However, FVIII was increased in patients with severe asthma attack Asthma is a disease in which many immune cells play a role, one of which is the platelet Distinctions in platelet secretion profiles and plasma levels of vWF and FVIII provide evidence that coagulation mechanisms might be critical for asthma pathogenesis. Blood Coagul Fibrinolysis 25:738-744 2014 (C) Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.