Antithrombin/HCII-depleted plasma was mixed with various percentages of normal plasma (upper right corner of A–F) prior to dilution and factor Xa-initiated thrombin generation assays as described in Fig 1. Assays were performed in the absence (solid line) or presence of 5 u/ml UFH (dotted line), enoxaparin (dashed/dotted line), or dalteparin (dashed line). Shown are curves from one of three sets of experiments (A–F) and the average change in lag time, compared to control, as a function of normal plasma concentration, from all three experiments (G, left panel; mean ± S.D). The right panel in (G) is an expanded view of the region indicated by dashed lines included to visualize the pro- and anti-coagulant activities of enoxaparin and dalteparin in 0.5%–2% normal plasma in comparison to UFH. UFH, unfractionated heparin; HCII, heparin cofactor II.