Representative differential interference contrast images of adult and neonatal platelet aggregates formed on coverslips coated with 100 μg/mL von Willebrand factor (VWF) (A) or 100 μg/mL fibrillar collagen (B). Adult and neonatal citrated whole blood were incubated with a glycoprotein (GP) IIbIIIa inhibitor (eptifibatide; 20 μg/mL), a GPIb function blocking antibody (6D1; 20 μg/mL), or vehicle for 10 min at 25°C and then treated with thrombin receptor activator peptide-6 (TRAP-6; 10 μM), collagen related peptide (CRP; 10 μg/mL), adenosine 5′-diphosphate (ADP) + U46619 (10 μM), ristocetin (1 mg/mL), or vehicle for 10 min. Mean volume of adult and neonatal platelet aggregates positive for CD62P-FITC formed on coverslips coated with VWF (C) or fibrillar collagen (D). Data are represented as mean ± SEM; Nadult = 3 and Nneonate = 3; *P < 0.05 with respect to vehicle treated samples.