In the tail bleeding assay, A/J mice did not have changes in bleeding time, but rebleeding time was higher compared to B6 mice. In our study, Plg-/- mice had increased bleeding time, PAI-1-/- had decreased rebleeding time, and uPA-/- mice had an increased bleeding time similar to the Plg-/- mice (J. Hoover-Plow, A. Shchurin, and E. Hart, unpublished results). Increased bleeding or rebleeding times have not been reported in any of the Plg network targeted mice. Matsuno et al [32] reported no difference in bleeding time for tPA-/-, uPA-/-, PAI-1-/- mice compared to WT mice, and the assay was similar, but the tail clip segment was considerably shorter and bleeding times reduced compared to the times reported in our study. Bleeding time has not been previously reported for Plg-/- mice. We have found similar values for Plg-/- mice in a 50%B6:50%129 background (J. Hoover-Plow, A. Shchurin, and E. Hart, unpublished results). The results of this study suggest that not only is bleeding time genetically determined by background, but also that tail rebleeding time is genetically determined.