DISEASE CHARACTERISTICS: Histologically confirmed advanced colorectal cancer No more than 2 prior chemotherapy regimens including fluorouracil and/or irinotecan (relapse within 6 months of adjuvant therapy is considered 1 prior regimen) Measurable disease

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-1 Life expectancy: At least 6 months Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 mg/dL SGOT no greater than 5 times upper limit of normal (ULN) Alkaline phosphatase no greater than 5 times ULN No significant hepatic dysfunction Renal: Creatinine no greater than 1.5 mg/dL Creatinine clearance at least 50 mL/min Cardiovascular: No significant cardiovascular dysfunction Neurologic: No dementia or altered mental status that would preclude informed consent No grade 3 motor or sensory neuropathy No significant neurologic dysfunction Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for 6 months after study No malabsorption syndrome or disease significantly affecting gastrointestinal function that would preclude absorption of eniluracil or fluorouracil No active infection requiring systemic therapy within

1 week of study No known platinum allergy No significant endocrine dysfunction

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: See Disease Characteristics Recovered from prior chemotherapy Endocrine therapy: Not specified Radiotherapy: Recovered from prior radiotherapy Surgery: No major resection of the stomach or proximal small bowel that would preclude absorption of eniluracil or fluorouracil