Abstract High molecular weight kininogen (HK) plays an important role in the assembly of the plasma kallikrein-kinin system. While the human genome contains a single copy of the kininogen gene, three copies exist in the rat (one encoding K-kininogen and two encoding T-kininogen). Here, we confirm that the mouse genome contains two homologous kininogen genes, mKng1 and mKng2. These genes are located on chromosome 16 in a head to head orientation with ∼ 30 kB intervening sequence, and are expressed in a tissue-specific manner. To determine the roles of these genes in murine development and physiology, we disrupted mKng1, which is expressed primarily in the liver. mKng1−/ − mice were viable, and immunoblotting using anti-bradykinin antibodies indicated a marked reduction in plasma HK and low molecular weight kininogen (LK), as well as ΔmHK-D5, a novel kininogen isoform that lacks kininogen domain 5. Clotting studies were also consistent with marked HK deficiency. Moreover, despite normal tail vein bleeding times, mKng1−/− mice displayed a significantly prolonged time to carotid artery occlusion following Rose Bengal administration and laser induced arterial injury. These results suggest that a single gene, mKng1, is responsible for production of plasma kininogen, and that plasma high molecular weight kininogen may contribute to induced arterial thrombosis in mice.