Microaggregate formation on stimulation of washed αIIbβ3-inhibited platelets by collagen. Platelets pretreated with dRGDW (200 μM) were stimulated with collagen (4 μg/mL; A-C) with purified coagulation factors VIIa, X, prothrombin, and fibrinogen (D-F) or with the combination (G-I) in an aggregometry setup as described in Figure 1. At time points 0 (A,D,G), 2 (B,E,H), and 10 minutes (C,F,I) samples were taken, fixed with glutaraldehyde, spun down on a glass coverslip, and stained with May-Grünwald/Giemsa. The coverslips were examined by light microscopy (original magnification, × 400).