PECAM-1 suppresses VWF binding-induced thrombus formation. Mepacrine-labeled wild-type and PECAM-1-deficient platelets were placed in parallel-plate flow chambers and subjected to arterial wall shear rates of (A) 600^s-1, (B) 800^s-1, and (C) 1500^s-1 over glass slides that had been coated with huVWF. Images were acquired continuously, captured, and digitized. At 600^s-1 and 800^s-1 but not at 1500^s-1, PECAM-1-negative platelets formed markedly larger thrombi, especially at 1 to 2 minutes following the initiation of flow, than did wild-type, PECAM-1-positive platelets.