This protocol will evaluate the activity of 5-Fluorouracil (FUra) given as a 1 hour infusion in combination with leucovorin (LV) and interferon IFN alpha-2a in patients with advanced, measurable colorectal cancer. IFN alpha-2a will be given at 5 million U/m(2) SC days 1-6; LV, 200 mg/m(2), will be given as a short infusion over 30 minutes days 2-6, followed immediately by a 1 hour IV infusion of FUra days 2-6. The starting dose of FUra will be 425 mg/m(2)/d(1). Cycles will be repeated at three week intervals provided that the granulocyte count and platelet count have recovered to &gte; 1200/microL and &gte; 80,000/microL, respectively, and all non-hematologic toxicity has resolved. The dose of FUra will be adjusted according to individual tolerance. Preliminary experience with FUra given as a 1 hour infusion suggests that it is less toxic. The primary goal of this study is to determine if this less toxic regimen retains clinical antitumor activity. FUra plasma samples will be obtained the initial cycle at 50 and 55 minutes during the first 1 hour infusion of FUra to permit documentation of achieved plasma levels and to permit correlation between FUra pharmacokinetics and clinical toxicity and/or response. Pharmacokinetic sampling will be repeated if the dose of FUra is increased or decreased in subsequent cycles.