In a previous study on 42 patients with acute deep vein thrombosis, randomly allocated to treatment with streptokinase or heparin, we found that 71.4% of the streptokinase-treated patients achieved phlebographically significant thrombolysis as compared to 23.8% in the heparin group. These patients have been reevaluated after a mean observation period of 6 1/2 years. Seven patients had died and there were no other drop-outs. Thus, 35 patients were subjected to the follow-up study consisting of phlebography and clinical examination. The evaluations were performed without knowledge of the initial therapy. Seven patients had phlebographically normal veins, and all belonged to the streptokinase group. This difference between the treatment groups is statistically highly significant (p less than 0.01). At clinical examination, 13 of the 17 patients in the streptokinase group had normal legs and 4 exhibited moderate postthrombotic changes. In contrast, 3 of the heparin-treated patients showed serious postthrombotic changes with open leg ulcers, and only 6 of 18 patients in this group had normal legs. The present results strongly support the assumption that streptokinase therapy is the best treatment at present in patients with acute deep vein thrombosis. This has been shown for the initial thrombolysis, and now also for the avoidance of late postthrombotic changes.