Progression of thrombus growth in 2-stage experiments, first with perfusion of untreated blood over collagen type I fibrils at 1,500 s⁻¹ for 100 seconds, then continuing without interruption at 300 or 1,500 s⁻¹ with blood containing either buffer (Control) or specific monoclonal antibodies, as indicated. Antibodies were incubated in blood for 10 minutes before initiating perfusion. (A) Stacks of z sections labeledA show thrombi formed after 100 seconds of perfusion with blood containing no antibody at wall shear rate of 1,500 s⁻¹; those labeled B show the growth of thrombi after an additional 740 seconds of perfusion at 300 s⁻¹with blood containing either buffer or the indicated antibodies (total perfusion time, 840 seconds). The effect of the antibodies in limiting increase in thrombus height, as clearly seen, is representative of the results observed in all experiments. (B) Thrombus volume was measured at the indicated cumulative perfusion times in these two-stage experiments. Bars are identified according to the type of inhibitor used in the second stage, but perfusion for the first 100 seconds was always performed with untreated blood. The results are expressed as mean ± SEM of between 4 and 10 experiments for the different conditions tested. Note that experiments at the shear rate of 1,500 s⁻¹ were terminated after collecting z sections at 420 seconds, since thrombi had already reached a large volume in control blood. Experiments with the combination of anti-GP Ib and anti-_IIbβ₃ monoclonal antibodies were not performed at 1,500 s⁻¹ since at this shear rate each individual antibody completely prevented thrombus growth as compared to the volume attained after the initial perfusion for 100 seconds with untreated blood.