Tachykinins and their receptor are important for normal thrombus formation. Whole blood from drug-free donors (A-C) in the presence of NK1 antagonist, L733060 (10 μM), or blood obtained from NK1-deficient mice or litter-matched controls (D-F), or TAC1-deficient mice or control mice (G-I), was perfused through collagen coated capillaries at a sheer rate of 1000 s⁻¹. Pictures of the thrombi were taken using confocal microscopy (A,D,G), the volume of the thrombi quantified (B,E,H), and protein concentration of the thrombi measured (C,F,I). Numeric data represent means plus or minus SEM. n = 3 (B,C), 8 (E), 6 (F), and 9 (H,I). *P < .05; **P < .01; ***P < .001.