The efficacy of the local delivery of an antithrombotic drug in preventing thrombosis and enabling thrombolysis was investigated in 29 dogs. An antithrombotic drug (heparin, 25U/kg), or an antithrombin (argatroban, 0.05 mg/kg) was infused into injured canine iliac arteries, using a double-occlusion balloon catheter, and the preventive effect of the drug was evaluated. Local delivery of low-dose tissuetype plasminogen activator (t-PA; Tisokinase, 50 000 U; Kowa, Nagoya and Asahi Chemical Industries, Fuji, Japan) into thrombosed canine iliac arteries, using the same catheter, or intravenous infusion of low-dose or high-dose t-PA (30 000U/kg), was also performed. Angiographically, stenotic thrombosis was 2% by local delivery of argatroban and 7% by local delivery of heparin (P < 0.01="" vs="" each="" control;="" 47%="" and="" 51%="" respectively).="" thrombotic="" stenosis,="" as="" observed="" by="" angiography,="" decreased="" from="" 91%="" to="" 9%="" after="" local="" delivery="" of="" t-pa,="" and="" from="" 94%="" to="" 52%="" in="" controls.="" local="" delivery="" of="" t-pa="" effectively="" reduced="" the="" thrombus="" size="">P < 0.01="" vs="" control).="" after="" systemic="" intravenous="" delivery="" of="" low-dose="" t-pa,="" no="" reduction="" of="" residual="" thrombotic="" stenosis,="" was="" observed.="" reduction="" of="" residual="" thrombotic="" stenosis="" after="" intravenous="" delivery="" of="" high-dose="" t-pa,="" was="" similar="" to="" that="" achieved="" by="" local="" delivery="" of="" the="" drug.="" angioscopy="" demonstrated="" a="" similar="" trend.="" high-dose="" drug="" delivery="" reduced="" systemic="" coagulability.="" local="" delivery="" of="" an="" antithrombotic="" drug,="" using="" a="" double-occlusion="" balloon="" catheter,="" effectively="" prevented="" thrombus="" formation,="" and="" local="" delivery="" of="" t-pa="" induced="" thrombolysis="" without="" exerting="" a="" significant="" influence="" on="">