DISEASE CHARACTERISTICS: Histologically confirmed metastatic colorectal cancer Measurable disease No CNS metastases or carcinomatous meningitis

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: At least 12 weeks Hematopoietic: Granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 9.0 g/dL Hepatic: Bilirubin no greater than 2.0 mg/dL (regardless of liver involvement secondary to tumor) AST no greater than 3 times upper limit of normal (ULN) (no greater than 5 times ULN if liver involvement) Renal: Creatinine no greater than 2.0 mg/dL Cardiovascular: No history of myocardial infarction in the last 6 months No congestive heart failure No cerebrovascular disease requiring therapy Other: No prior malignancy within 5 years except adequately treated basal cell or squamous cell skin cancer or in situ cervical cancer No uncontrolled diabetes mellitus (defined as random blood sugar at least 200 mg/dL) No active or uncontrolled infection No other severe concurrent disease No psychiatric disorders that would interfere with study

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since any prior biologic therapy for cancer Chemotherapy: At least 4 weeks since any prior chemotherapy for cancer No prior irinotecan Endocrine therapy: At least 4 weeks since any prior endocrine therapy for cancer Radiotherapy: Prior radiotherapy to pelvis for colorectal cancer is allowed At least 6 weeks since radiotherapy to other areas if measurable lesions are present outside of the radiation field Surgery: Not specified Other: At least 24 hours since antihypertensive medication