Twenty-seven patients with deep vein thrombosis whose primary therapy was randomized between streptokinase and heparin were reevaluated clinically and by ascending venography after a mean period of 7 months. Normal venograms were found in 6 (40%) of the streptokinase-treated patients and in 1 patient (8%) who had heparin therapy. Segmental valve preservation was found in 1 patient from each group. All patients with complete or partial valve preservation became asymptomatic. Vein recanalization without preservation of valves occurred in 18 patients: 8 (54%) of those on streptokinase, and 10 (83%) of those on heparin. At the time of follow-up, 11 of these 18 patients, including 8 who had had prior thrombosis, reported peripheral edema; the postphlebitic syndrome developed in 1. Factors favoring a good outcome of acute venous thrombosis were (1) no prior thrombotic disease, (2) localized thrombosis, and (3) prompt streptokinase therapy.