OUTLINE: This is a dose escalation study. Patients are entered to one of two treatment arms: Arm I (Saltz regimen): Patients receive irinotecan IV over 90 minutes, leucovorin calcium IV, and fluorouracil IV on days 1, 8, 15, and 22, followed by oxaliplatin IV over 2 hours on days 1 and 15. Courses repeat every 6 weeks. Arm II (Mayo regimen): Patients receive irinotecan IV over 90 minutes and oxaliplatin IV over 2 hours on day 1, followed by leucovorin calcium IV and fluorouracil IV over 90 minutes on days 2-5. Courses repeat every 3 weeks. Cohorts of 3-6 patients receive escalating doses of fluorouracil (one of two treatment doses for arm II), and one of two treatment doses of irinotecan and oxaliplatin until the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose preceding that at which 2 of 6 patients experience dose limiting toxicity. Patients are followed for 3 months.