Five patients with acute massive pulmonary embolism were treated with streptokinase administered via the pulmonary artery as close as possible to the embolus. Streptokinase (Awelysin) was infused at a loading dose of 250,000 IU followed by a maintenance dose of 100,000 IU/hour under haemodynamic and angiographic control. In four of five patients (two patients with cardiogenic shock) the clinical signs, pulmonary artery pressure and the angiographic findings improved or they normalised within 5-12 hours. In one patient with recurrent embolisation over three weeks the clinical condition improved gradually, although the angiographic findings improved only slightly. The results demonstrate that local thrombolysis of acute massive pulmonary embolism is a highly effective form of treatment.