Patients with symptoms of deep vein thrombosis for less than 10 days were treated with a standard dose of heparin. In the open label phase of the trial, 11 patients received 100 mg rt-PA on the first day and 50 mg on the subsequent day in an 8 hour infusion. In the double-blind phase, 8 patients were randomized to the same rt-PA regimen, 6 patients to an infusion of 50 mg rt-PA over 8 hours on days 1 and 2, and 7 patients to placebo infusions. The mean change in venographic score in all patients treated with rt-PA plus heparin is -3.8 units compared to -0.6 units in patients treated with heparin alone (p = 0.06). Bleeding complications classified as major were noted in 8/25 patients receiving the combined treatment.