Our investigations have indicated that clearance of GPIb/IX receptors from exposed surfaces to interior membranes of thrombin (T)-activated platelets(Pl), as proposed by others, is unlikely. In this study washed platelet suspensions with or without EDTA were treated with either T (0.2 - 1.0 U/ml) or 25-100 μM TRAP-14 mer peptide for 5′ and 10′, then immediately exposed to formvar grids in a flat perfusion chamber at a shear rate of 1000 s-1 for 5′, 10′ and 15′. Control Pl not treated with either agonist were exposed to high shear conditions for the same intervals. After completion of high shear exposure, grids were fixed by perfusion in 0.01% glutaraldehyde. Pl were then incubated with either bovine vWF followed by anti-vWF and protein A gold (PAG) or a cocktail of AP1 and 6D1, then goat anti-mouse IgG coupled to gold. Electron micrographs of seven identical-sized areas on each of 5-10 platelets from every experiment photographed at the same magnification were evaluated by hand counts and with the Metamorph 2.0 Imaging System software to determine the frequency of GPIb/IX receptors on suspension activated, surface sheared Pl and the organization of vWF. Statistical analysis revealed no differences in the frequency of GPIb/IX receptors (p > 0.85) on dendritic and spread Pl exposed or not to activation in suspension and then to high shear. The results indicate that Pl GPIb/IX receptors able to bind vWF are not cleared from the surface to internal membrane systems following combined suspension and high shear activation.