Deficiency in FXII or FXI abrogates collagen enhancement of thrombin generation. Plasma (PPP) from wild-type, FXII^−/−, or FXI^−/− mice was supplemented with washed platelets, which were pooled from wild types (10⁸ platelets/mL, fc). Samples were pretreated with collagen type I/H (5 μg/mL), vehicle solvent (control), and/or FVIIai (100 nM), as indicated. Thrombin generation was triggered by CaCl₂ without (A-B) or with (C) tissue factor (1 pM). Shown are representative thrombin generation curves (A) and thrombin peak height (B,C); thrombin is expressed as arbitrary activity units. Note the impairment of collagen effects with FXII^−/− or FXI^−/− plasma. Mean ± SEM; n = 4-5; *P < .05 vs control.