The role of non-toxic purified preparations of human fibrinolysin as an adjunct to the surgical treatment of thromboembolic disease was evaluated in 37 patients. In each case surgical intervention was carried out in response to the usual indications; in addition, each patient received a preparation of fibrinolysin by venoclysis. In many cases the subjective evidence of improvement was corroborated by objective evidence in the form of arteriograms or the return of arterial pulses. The failures included patients with old organized emboli or with thromboses that had existed longer, than 48 hours. The optimum duration of fibrinolysin therapy was estimated to be about 30 hours. In order to prevent rethrombosis it was necessary to maintain the patient subsequently on heparin therapy.