PURPOSE: This phase II trial investigated the safety and efficacy of two doses of bevacizumab, a monoclonal antibody to vascular endothelial growth factor, plus fluorouracil (FU)/leucovorin (LV) versus FU/LV alone in patients with metastatic colorectal cancer. PATIENTS AND METHODS: One hundred four previously untreated patients with measurable metastatic colorectal cancer were randomly assigned to one of the following three treatment groups: 36 to FU (500 mg/m(2))/LV (500 mg/m(2)) alone, 35 to FU/LV + low-dose bevacizumab (5 mg/kg every 2 weeks), and 33 to FU/LV + high-dose bevacizumab (10 mg/kg every 2 weeks). FU/LV was given weekly for the first 6 weeks of each 8-week cycle. RESULTS: Compared with the FU/LV control arm, treatment with bevacizumab (at both dose levels) plus FU/LV resulted in higher response rates (control arm, 17%, 95% confidence interval [CI], 7% to 34%; low-dose arm, 40%, 95% CI, 24% to 58%; high-dose arm, 24%, 95% CI, 12% to 43%), longer median time to disease progression (control arm, 5.2 months, 95% CI, 3.5 to 5.6 months; low-dose arm, 9.0 months, 95% CI, 5.8 to 10.9 months; high-dose arm, 7.2 months, 95% CI, 3.8 to 9.2 months), and longer median survival (control arm, 13.8 months; 95% CI, 9.1 to 23.0 months; low-dose arm, 21.5 months, 95% CI, 17.3 to undetermined; high-dose arm, 16.1 months; 95% CI, 11.0 to 20.7 months). After cross-over, two of 22 patients had a partial response to bevacizumab alone. Thrombosis was the most significant adverse event and was fatal in one patient. Hypertension, proteinuria, and epistaxis were other potential safety concerns. CONCLUSION: The encouraging results of this randomized trial support further study of bevacizumab 5 mg/kg plus chemotherapy as first-line therapy for metastatic colorectal cancer.