1. Assay methods were developed for key components of the tissue factor pathway of blood coagulation, namely Factor V, Factor VII and Factor X. Using these assays, plasma from healthy laying hens, cockerels and broilers was shown to contain functional and equivalent amounts of each of these clotting factors. 2. The plasma activities for Factor V, Factor VII and Factor X can only be accurately determined when chicken tissue factor is used to initiate the coagulation mechanism in poultry plasma. Neither human tissue factor nor rabbit tissue factor forms a fully functional enzyme reactive complex with chicken Factor VII. 3. The overall tissue factor pathway coagulation mechanism was evaluated in plasma from laying hens, cockerels and broilers using the one-stage prothrombin time assay. As long as sufficient tissue factor was used, the overall clotting time results obtained with human recombinant tissue factor were not significantly different from those obtained with chicken tissue factor. 4. We conclude that poultry plasma does possess a fully functional tissue factor coagulation mechanism, but homologous chicken tissue factor must be used for in vitro assays of the components of this pathway.