OBJECTIVES: I. Determine the maximum tolerated dose (MTD) for the combination chemotherapy regimen of oxaliplatin plus irinotecan when both drugs are given once a week for four weeks, followed by a two week rest, in patients with metastatic gastrointestinal cancer. II. Evaluate the toxicities of this combination chemotherapy when administered in this manner. III. Determine the pharmacokinetics of platinum and irinotecan at the MTD for this combination chemotherapy in this patient population.