Tissue pathway factor inhibitor (TFPI) inactivation rates were determined by incubating TFPI and bacteria for various times at 37°C, then quantifying TFPI activity in clotting assays. Remaining TFPI activities were determined by reference to standard curves using purified TFPI. Experimental conditions resulting in insufficient plasmin or FVIIa for accurate determination of activation rates are listed as not detectable (ND). The lower limit of detection for both assays corresponded to an activation rate of approximately 50 molecules/minute per cfu. Results are mean plus SEM (n = 3).