Mouse platelets do not respond to Trap6 (PAR1-activating peptide), and vascular injection of Trap6 is not lethal to mice. The mouse platelet response to Trap6 was evaluated using (A) whole blood clotting time (n = 5, individual controls were used for the 2 peptides because of limited blood volume), (B) platelet fibrinogen binding detected by flow cytometry in citrated blood (n = 3), and (C) citrated whole blood platelet aggregation (using Multiplate; n = 4). No platelet activation was detected on addition of 30 µM Trap6 peptide. PAR4-AP was used as a positive control at 300/170 µM and led to considerable platelet activation in all experiments. It is well known that PAR4-AP is required at higher concentrations to achieve full activation. (D) Survival of mice that were challenged by injections with Trap6 or PAR4-AP into the jugular vein. In the group receiving 44.8 µg PAR4-AP/g body weight, 4 of 15 animals died, whereas none died in the groups receiving Trap6 (low: 0.7 µg/g body weight; medium: 2.8 µg/g body weight; high: 11.2 µg/g body weight) or saline (n = 15 per group; P = .035 vs PAR4-AP). The x-axis represents time in minutes after administration of substance. All measurements (except in D) are presented as mean ± SD. Statistical testing was performed with (A-B) ANOVA and Tukey’s post hoc test, and (D) survival time differences between treatment groups were analyzed by log-rank analysis, both in a total model and for combinations of the different groups.