Local thrombolytic treatment of peripheral arterial occlusions, which has been accepted as a therapeutic alternative to surgical treatment, is not always successful. One of the reasons for unsuccessful thrombolytic treatment might be a low concentration of plasminogen in the thrombus or insufficient activation of the thrombolytic system. Therefore the purpose of this study was to determine whether the success of local treatment of peripheral arterial occlusions of lower extremities with streptokinase could be improved by enriching the thrombus with exogenous plasminogen and furthermore, if the therapeutic success depends on a systemic fibrinolytic effect. In a prospective randomized study two groups of patients with acute and subacute arterial occlusions of the lower limbs (Stage III, IV) were treated with a continuous infusion of local low dose of streptokinase (SK). The first group (45 patients, mean age 73 years) was treated with SK only (3750 IU/hour) (SK group). While the patients in the second group (43 patients, mean age 72 years) received exogenous lys-plasminogen (7.5 mg) before application of SK in thrombi (SK-Plg group). The treatment was successful in 69% (31 out of 45 patients) of the SK group and in 77% (33 out of 43 patients) of the SK-Plg group. Although lysis of thrombi was observed more frequently in the SK-Plg group than in the SK-group, the clinical outcome was comparable between groups. In successfully treated patients from the SK-Plg group the duration of treatment was significantly shorter than in the SK group (33 +/- 8 hr vs. 53 +/- 11 hr, p < 0.01). A significant decrease of fibrinogen concentration as an indicator of activation of fibrinolysis was not observed in the majority of treated patients. On the other hand, in successfully treated patients of both groups, the following was observed: 24 hour after the beginning of treatment, euglobulin clot lysis times were shortened to half of baselines values, and the plasminogen concentration was also significantly reduced (to 55% of the baseline value). In unsuccessfully treated patients no significant changes in fibrinolytic parameters were observed. The results of our study indicated that enrichment of the thrombus with exogenous plasminogen does not significantly improve the percentage of successful recanalization of peripheral arteries with a local low dose of SK, but significantly shortens the duration of treatment up to reperfusion. The study also showed that in local thrombolysis for the treatment of arterial occlusion a certain degree of systemic activation of the fibrinolytic system is essential for successful dissolution of the thrombi.