OUTLINE: This is a randomized, open label, multicenter study. Patients are stratified according to performance status (ECOG 0 vs 1), site of primary disease (colon vs rectum), measurable or evaluable disease, and prior fluorouracil adjuvant chemotherapy (none vs at least 1 dose). Patients are randomized to one of two treatment arms: Arm I: Patients receive leucovorin calcium IV over 2 hours and fluorouracil IV bolus 1 hour into leucovorin calcium administration weekly for 6 weeks. Arm II: Patients receive leucovorin calcium IV over 2 hours and fluorouracil IV bolus 1 hour into leucovorin calcium administration weekly for 6 weeks, plus SU5416 twice weekly for 8 weeks. Treatment repeats every 8 weeks in the absence of disease progression or unacceptable toxicity. Quality of life is assessed prior to study, at weeks 4 and 8 of each course, and then post study. Patients are followed post study at one month and then every 2 months until death.