* Histologically or cytologically proven metastatic colorectal cancer
* Prior surgery required
* No prior treatment for metastatic disease
* Disease progression while on fluorouracil adjuvant therapy
* Bidimensionally measurable disease
* Age: Over 18
* Performance status: SWOG 0-2
* Hematopoietic: Platelet count at least 100,000/mm3, Absolute granulocyte count at least 1,500/mm3
* Hepatic: Bilirubin no greater than 1.5 times upper limit of normal (ULN) SGOT or SGPT no greater than 3 times ULN (no greater than 5 times ULN if liver involvement)
* Renal: Creatinine clearance at least 50 mL/min
* Other: Must be able to swallow and retain oral medications No nutritional support by gastrostomy feeding tube or parenteral support No intractable vomiting or nausea
* Patients with history of prior malignancy must be currently disease free and off all therapy for that malignancy
* Not pregnant or nursing Fertile patients must use effective contraception
* Biologic therapy: No concurrent immunotherapy Chemotherapy; At least 3 weeks since prior chemotherapy and recovered; No concurrent flucytosine; No other concurrent chemotherapy
* Endocrine therapy: No concurrent hormonal therapy
* Radiotherapy: Prior adjuvant pelvic radiation or radiation to one area of recurrence allowed At least 4 weeks since prior radiotherapy and recovered Total area of bone marrow irradiation must not exceed 25% No concurrent radiotherapy
* Surgery: At least 2 weeks since prior surgery for colorectal cancer and recovered No prior resection of the stomach or small intestine
* Other: No other concurrent anticancer therapy