Background: In sepsis, extracellular ATP, secreted by activated platelets and leukocytes, may contribute to the crosstalk between hemostasis and inflammation. Previously, we showed that, in addition to their role in platelet activation, ATP-gated P2X1 ion channels are involved in promoting neutrophil chemotaxis. Objectives: To elucidate the contribution of P2X1 ion channels to sepsis and the associated disturbance of hemostasis. Methods: We used P2X1)/) mice in a model of lipopolysaccharide ( LPS)-induced sepsis. Hemostasis and inflammation parameters were analyzed together with outcome. Mechanisms were further studied ex vivo with mouse and human blood or isolated neutrophils and monocytes. Results: P2X1)/) mice were more susceptible to LPSinduced shock than wild-type mice, despite normal cytokine production. Plasma levels of thrombin-antithrombin complexes were higher, thrombocytopenia was worsened, and whole blood coagulation time was markedly reduced, pointing to aggravated hemostasis disturbance in the absence of P2X1. However, whole blood platelet aggregation occurred normally, and P2X1)/) macrophages displayed normal levels of total tissue factor activity. We found that P2X1)/) neutrophils produced higher amounts of reactive oxygen species. Increased amounts of myeloperoxidase were released in the blood of LPS-treated P2X1)/) mice, and circulating neutrophils and monocytes expressed higher levels of CD11b. Neutrophil accumulation in the lungs was also significantly augmented, as was lipid peroxidation in the liver. Desensitization of P2X(1) ion channels led to increased activation of human neutrophils and enhanced formation of platelet- leukocyte aggregates. Conclusions: P2X1 ion channels play a protective role in endotoxemia by negatively regulating systemic neutrophil activation, thereby limiting the oxidative response, coagulation, and organ damage.