The effect of varying phospholipid concentrations on thrombin generation in plasma. Thrombin generation was initiated in normal pooled plasma with 3.5 pM tissue factor (A) or 250 pM factor Xa (B), 16 mM CaCl₂, and indicated concentrations of phospholipid vesicles (20/60/20 DOPS/DOPC/DOPE; 100, 25, 5 or 1 μM final concentrations) in the presence (•) or absence (○) of antibodies against protein S. All plasma mixtures contained antibodies against protein C. Thrombin generation was quantified with the fluorogenic substrate I-1140 as described in “Materials and methods.”