14E11 and O1A6 individually block thrombin/fibrin generation on collagen. Anticoagulated whole blood (CTI, 4 μg/mL) was treated with FXI antibody 14E11 or O1A6 (20 μg/mL) and was perfused over the collagen surface at 100 s⁻¹ under constant flow rate condition (constant Q). FXI antibodies efficiently abolished thrombin and fibrin generation on collagen surface without affecting platelet deposition. (A) Dynamics of platelet deposition and (B) generation of fibrin and (C) thrombin based on 5 clotting events (± standard deviation [SD], shaded). End point images are shown for platelet (red; panel A inset), fibrin (green; panel B inset), and thrombin (cyan; panel C inset) on collagen surface (white arrows indicate flow direction; scale bar = 50 μm). (D) Final platelet, fibrin, and thrombin fluorescence (t = 600 s) was normalized to control. Adding FXI antibodies caused more than 90% reduction in final fibrin and thrombin generation. **P < .01; ***P < .005. n.s., not significant.