A randomized prospective trial was undertaken to compare intraarterial administration of recombinant human tissue-type plasminogen activator (rt-PA) with urokinase (UK) in 32 patients with peripheral arterial or bypass graft occlusions. Sixteen patients were randomized to receive rt-PA and 16 to receive UK. The rt-PA dose was administered as a 10-mg bolus into the thrombus, followed by 5 mg/h for up to 24 hours. The UK dose was administered as a 60,000 IU bolus into the thrombus, followed by 240,000 IU/h for 2 hours, 120,000 IU/h for 2 hours, and 60,000 IU/h for up to 20 hours. Serial arteriograms were obtained at baseline and at 4, 8 or 16, and 24 hours. The endpoint was defined as 95% of greater clot lysis. The cumulative numbers of patients with successful thrombolysis (rt-PA vs UK) were four vs none at 4 hours, seven vs one at 8 hours, seven vs three at 16 hours, and eight vs six at 24 hours. Lysis occurred more rapidly in the rt-PA group (P = .04). Major bleeding complications occurred in five rt-PA patients and two UK patients (P = .39). At 24 hours, fibrinogen levels were significantly lower in the rt-PA group than in the UK group (P = .01). There was no apparent difference in 30-day clinical success.