Kinetic analysis of the tissue factor (TF)-factor VIIa (FVIIa) binding interaction is helpful in investigating the structure-function relationships of TF-FVIIa. However, a wide variation exists among the reported binding affinities of FVIIa to TF, particularly when comparing KD values obtained from functional activity assays versus ligand binding studies. Surface plasmon resonance (SPR) technique was used frequently to investigate binding kinetics of FVIIa to TF in a lipid-free environment. In the present study we used TF embedded in a phospholipid bilayer for determining binding kinectis using SPR. The data revealed that FVIIa had a much higher binding affinity (>100-fold) for TF embedded in the phospholiid bilayer than TF in a lipid-free environment, approaching the KD values that were noted in the enzymatic activity assays. The present data suggest that SPR binding studies using TF embedded in phospholipids is more appropriate for investigating how FVIIa (or FVIIa mutants/derivatives) may interact with TF in physiological settings.