In a series of 447 patients with single vessel angioplasty, 27 (6.0%) had acute thrombotic occlusion early after the procedure. They were treated with combined intracoronary (20 mg)/intravenous (50 mg) thrombolysis with recombinant tissue-type plasminogen activator (rt-PA) and repeat mild balloon inflations. Reopening of the vessel was achieved in 22 patients (81.5%). Follow-up coronary angiography 24 to 36 h later revealed reocclusion in 12 patients (54.5%). Thrombin levels measured as thrombin-antithrombin-III complex in patients with successful thrombolysis and persistent patency decreased from 8.5 ± 11.4 μg/liter at baseline to 3.5 ± 1.4 μg/liter 120 min after the start of thromboiysis; these levels increased from 9.4 ± 15.0 μg/ liter at baseline to 15.7 ± 13.5 μg/liter 120 min after the start of thromboiysis in the patients with unsuccessful thrombolysis or early reocclusion (p < 0.05). When a borderline value for thrombin-antithrombin-III complex level of 6 μg/liter was selected to separate the two groups of patients, patients with an unfavorable clinical course were identified 120 min after the start of thrombolysis by levels >6 μg/liter (sensitivity 100%, specificity 92.8%). Thus, after abrupt thrombotic vessel closure during coronary angioplasty, the short-term results of thrombolysis seem to be governed by the release of thrombin. In two thirds of patients, however, the thrombin release cannot be suppressed by concomitant aspirin and heparin therapy. Even after successful reopening of the vessel these patients should therefore undergo immediate aortocoronary bypass grafting. © 1990.