Using the tail bleeding/rebleeding assay as a surrogate marker for hemostasis and thrombosis, the CSS were screened. The bleeding times (Figure 4A) for the B6 and the A/J mice were not different, but 6six of the strains, B6-Chr5, 6, 8, 14, 15, and YA/J, had lower (P < 0.002) bleeding times (49–79 seconds) compared to the value for the B6 mice (121 sec). The rebleeding time (Figure 4B), determined as the time between bleeding cessation and initiation of the second bleeding, was markedly increased in the A/J mice compared to the B6 mice and two strains, B6-Chr11A/J (CSS-11) and B6-Chr17A/J (CSS-17), had significantly (P < 0.002) longer rebleeding times compared to the B6 mice that were similar to values from the A/J mice. Another strain, B6-Chr5A/J (CSS-5), approached significance at P < 0.008. The rebleeding time was stopped at 600 sec, and the percentage of mice with this value determined for the three strains: CSS-5–60%, CSS-11–60% and CSS-A17–46%. The percentage of B6 mice with a rebleeding time of 600 sec was 7% and for the A/J mice the percentage was 85%.