OBJECTIVES: I. Compare the efficacy of leucovorin calcium plus fluorouracil with either irinotecan or oxaliplatin in terms of progression free survival in patients with recurrent metastatic colorectal cancer. II. Compare the efficacy, tolerance, quality of life, and overall survival in this patient population.

OUTLINE: This is a randomized, multicenter study. Patients are stratified by participating institution and measurable or evaluable disease. Patients are randomized to receive either a 2 hour continuous infusion of irinotecan or a 2 hour continuous infusion of oxaliplatin on day 1. All patients receive a 2 hour continuous infusion of leucovorin calcium followed by IV bolus and 48 hour continuous infusion of fluorouracil on days 1 and 2. Courses are repeated every 2 weeks. Patients will receive the alternate treatment if disease progression or unacceptable toxicity occurs on their initial treatment. Patients are followed every 3 months after end of treatment.

PROJECTED ACCRUAL: This study will accrue a total of 109 patients per arm over approximately 18 months.

DISEASE CHARACTERISTICS: Histologically proven recurrent stage IV adenocarcinoma of the colon and rectum No CNS metastases Bidimensionally measurable lesion (at least 2 cm in dimension) or evaluable disease (as malignant ascites or bone metastases) as documented by CT or MRI Must be outside prior radiotherapy field

PATIENT CHARACTERISTICS: Age: 18 to 75 Performance status: WHO 0-2 Life expectancy: Greater than 3 months Hematopoietic: Absolute neutrophil count greater than 1,500/mm3 Platelet count greater than 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 times normal Alkaline phosphatase no greater than 3 times normal SGOT/SGPT no greater than 3 times normal Renal: Creatinine no greater than 1.5 mg/dL Cardiovascular: No uncontrolled congestive heart failure or angina pectoris in the past 6 months No hypertension or arrhythmia in the past 6 months Neurologic: No peripheral neuropathy No significant neurologic or psychiatric disorder Other: No complete or partial obstruction of the bowel No serious nonmalignant disease No active infection No second malignancy except in situ cervical carcinoma or nonmelanomatous skin carcinoma No chronic diarrhea Not pregnant or nursing Fertile women must use adequate contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: No prior immunotherapy for metastatic disease Chemotherapy: No prior chemotherapy for metastatic disease At least 6 months since prior adjuvant chemotherapy with no disease progression or after metastatic liver resection No prior chemotherapy with oxaliplatin or irinotecan Endocrine therapy: Not specified Radiotherapy: At least 2 weeks since prior radiotherapy Surgery: At least 2 weeks since surgery Other: At least 30 days since use of investigational agent