Inhibition of fibrinogen binding to α_IIbβ₃ decreases IAC-1 binding to adhering platelets under flow conditions. Anticoagulated whole human blood was perfused over a collagen-coated surface at a wall shear rate of 1000 s⁻¹. Postperfusion was performed with either FITC-labeled MOPC-21 (5 μg/mL), FITC-labeled Gi9 (5 μg/mL), or FITC-labeled IAC-1 (10 μg/mL). (A) Representative phase-contrast (left column) and fluorescence (right columns) microscopic images of adhered platelets after 4 minutes of perfusion in the presence (bottom row) or absence (top row) of aggrastat. Scale bars indicate 25 μm. (B) Platelet adhesion in the presence or absence of aggrastat, determined as a percentage of surface coverage. Data obtained from phase-contrast images are in black; fluorescence data of IAC-1–FITC images are in white. Data are expressed as the mean ± SE of 10 images of at least 3 independent experiments.