Thromboxane A2 (TXA2) has potent actions on platelet aggregation, vasoconstriction, as well as regulating renal hemodynamics. It plays a role in the pathogenesis of a number of disease states including myocardial infarction, thrombotic stroke, bronchial asthma and a variety of renal diseases. Besides its well-recognized role in hemostasis and thrombosis, thromboxane A2 synthase (TXAS) is proposed to be involved in thrombopoiesis and lymphocyte differentiation. To evaluate its various physiological roles, TXAS-deleted mice was generated by gene targeting. TXAS-/- mice had normal bone marrow megakaryocytes, blood platelet counts, and normal CD4 and CD8 lymphocyte counts in thymus and spleen. Platelets from TXAS-/- mice failed to aggregate or generate thromboxane B2 in response to arachidonic acid (AA) but produced increased PGE2, PGD2 and PGF2α. AA infusion caused a progressive drop of mean arterial pressure (MAP), cardiac arrest and death in WT mice, but did not induce shock in TXAS-/- mice, nor in WT and TXAS-/- mice treated with antagonist to the TP receptor. The TXAS-/- mice were able to maintain normal MAP upon AA insult when TP was present but were unable to do so when TP was blocked by an antagonist, suggesting a role of endoperoxide accumulation in influencing MAP. We also found that TXAS deletion can influence 15-HETE and LTB4 production from lipoxygenase pathway, suggested that TXA2 may regulate inflammatory mediator formation. We conclude that TXAS is not essential for thrombopoiesis and lymphocyte differentiation. Its deficiency causes a mild hemostatic defect and protects mice against arachidonate-induced shock and death. The TXAS-deleted mice will be valuable for investigating the roles of arachidonate metabolic shunt in various pathophysiological processes.