The primary cause of free flap failure remains vascular thrombosis at the microanastomosis site. Four-hour local infusion of tissue plasminogen activator (t-PA) has been proved to effectively lyse thromboses in microvascular studies of animals; however, rethrombosis occurs once the infusion of t-PA has been terminated. The present study was designed to examine the efficacy of 48 hours of a continous local t-PA infusion in maintaining long-term venous patency. Our previously described modified arterial inversion graft reanastomosed into the venous system was used in rabbits to form venous thrombi. Three mg of t-PA was infused over 48 hours in eleven rabbits. Seven of eleven grafts were patent at 48 hours and four remained patent at 1 week. In comparing the patency rates in this study with the overall patency rate using the modified arterial inversion graft model (1/22), there are statistically significant differences at both 48 hours (p < 0.001) and 7 days (p < 0.05). We conclude that lengthening the infusion time of t-PA may increase the long-term patency rate in this animal model.