Among the serious complications encountered with long-term, indwelling Silastic central venous catheters are catheter-induced intravascular thrombi. These thrombi are usually treated by removal of the catheter to prevent thrombus propagation, embolization, or infection. We treated ten patients with urokinase infusion who had experienced 12 incidents of induced intravascular thrombi. Catheter phlebography and two-dimensional echocardiography were used for diagnosis and follow-up. Eleven of the 12 episodes were treated successfully, with complete dissolution of the thrombus. One patient with a calcific thrombus had only partial clot lysis and required catheter removal. By utilizing urokinase infusion to treat Silastic catheter-induced intravascular thrombi, nine of ten central venous catheters were preserved and the possible need for thrombectomy was averted. No serious complications were encountered. In our experience, urokinase therapy has been an effective and safe method for treating Silastic catheter-induced intravascular thrombi.