PURPOSE: The Intergroup conducted this breast cancer adjuvant trial to compare an investigational 16-week regimen with cyclophosphamide, doxorubicin, and fluorouracil (5-FU; CAF). The 16-week regimen features greater doxorubicin and 5-FU dose-intensity than CAF and improved scheduling of antimetabolites with sequential methotrexate and 5-FU, as well as infusion 5-FU. PATIENTS AND METHODS: A total of 646 node-positive, receptor-negative patients were randomly assigned to receive either the 1 6-week regimen or six cycles of CAF. Breast cancer outcomes included recurrence as well as disease-free and overall survival. Toxicity was evaluated by the Common Toxicity Criteria (CTC). Treatment-related quality of life was assessed by the Breast Chemotherapy Questionnaire (BCQ) before, during, and 4 months after treatment in 163 patients. The trial was designed to use one-sided tests of significance for power calculations, but is now reported with both one-sided and the traditional two-sided tests of significance. RESULTS: At a median follow-up of 3.9 years, the estimated 4-year recurrence-free survival rate was 67.5% with the 16-week regimen versus 62.7% with CAF (P = .19, two-sided; P = .095, one-sided). The estimated 4-year survival rate was 78.1% with the 16-week regimen versus 71.4% with CAF (P = .10, two-sided; P = .05, one-sided). CAF produced significantly higher grades of leukopenia, granulocytopenia, and thrombocytopenia, as well as liver and cardiac toxicity, whereas the 16-week regimen produced significantly higher grades of anemia, nausea, stomatitis, and weight loss, as well as skin and neurotoxicity. There were three treatment-related deaths with CAF but none with the 16-week regimen. During treatment, quality of life declined significantly more with the 16-week regimen than CAF, but by 4 months posttreatment, there was no difference. CONCLUSION: The 16-week regimen produced marginally better breast cancer outcomes than CAF with similar toxicity but a greater reduction in during-treatment quality of life. The 16-week regimen should not be used instead of a standard-dose regimen without careful consideration of the 16-week regimen's pros and cons, which include its complicated schedule. It should probably not be tested further, but its antimetabolite schedules and frequent drug administration (ie, dose density) should be considered in the development of new regimens.