Schematic representation of the time course of thrombus formation and subsequent treatment. The time course indicates initiation of thrombus formation, thrombus maturation during the first 30 minutes, and the following 60 minutes of treatment. The duration of experiment extends for a total of 90 minutes, during which 7 separate blood samples are obtained at the indicated times. Thirty minutes were allowed for tissue factor exposed on the denuded aorta to produce a thrombus from rabbit whole blood containing radiolabeled rabbit fibrinogen. PTI or saline was administered immediately before obtaining the second blood sample at 30 minutes. After the blood sample was obtained at the 30-minute time point, but before the next blood sample at 35 minutes, a bolus of tPA or saline was administered and an infusion of each was initiated.