Effects of inhibitory antibodies and receptor antagonists on size distribution of platelet aggregates during thrombus formation. Histograms were obtained by image analysis of phase-contrast micrographs obtained from perfused collagen surfaces. Estimated numbers of platelets per feature were 1 to 2 ( ▦ ), 2 to 8 ( ▧ ), 8 to 40 (▥ ), 40 to 130 (▪), and more than 130 platelets (□). (A) Control. (B) 10B12 at 50 μg/mL. (C) 1C3 at 100 μg/mL. (D) ADP receptor and TxA₂ blockade. (E) 6F1 at 20 μg/mL. (F) GFOGER-GPP at 500 μg/mL. Data (A-F) are mean ± SE from 3 donors. Statistical significance compared with the control was established from contingency tables (χ² analysis).