Tissue factor pathway inhibitor (TFPI), a protease inhibitor that is present in free and lipoprotein-associated forms in plasma and that also occurs as an endothelial cell-associated form, can inhibit the initial reactions of the tissue factor-mediated coagulation pathway. Although a positive correlation between plasma TFPI activity and cholesterol concentration in human plasma has been demonstrated, levels of the various forms of TFPI, ie, the LDL/VLDL-associated form, the HDL-associated form, and the free form, have not yet been completely determined in hyperlipidemia. We therefore established a method for the measurement of each of these forms of TFPI in plasma by gel filtration of plasma in buffer containing 1 mol/L NaCl. The recovery of TFPI activity in the free form was markedly greater as assessed by the new method than the recovery reported when other methods have been used. We employed the new method to analyze TFPI activity in 19 hyperlipidemic patients and compared the results with those for normal control subjects. The level of LDL/VLDL-associated TFPI in hyperlipidemic patients was significantly increased compared with control subjects' levels (0.383 +/- 0.112 versus 0.237 +/- 0.077 U/mL), whereas the level of the free form of TFPI in hyperlipidemic patients was significantly decreased (0.381 +/- 0.132 versus 0.495 +/- 0.106 U/mL), the former being positively correlated with cholesterol level, while the latter was negatively correlated.(ABSTRACT TRUNCATED AT 250 WORDS)