DISEASE CHARACTERISTICS: Histologically or cytologically proven colorectal cancer with failure or relapse after at least 1 prior fluorouracil based chemotherapy regimen for advanced disease OR metastatic disease within 6 months after completion of adjuvant therapy No more than 1 prior fluorouracil based chemotherapy regimen for metastatic disease Prior oral fluorouracil or combinations of other drugs with fluorouracil allowed Prior adjuvant therapy with fluorouracil allowed and not counted as 1 regimen if given more than 1 year prior to study At least 1 bidimensionally measurable indicator lesion that has not been irradiated and has the following minimum dimensions: Skin nodule or superficial lymph node: 2 x 2 cm Lung lesion surrounded by aerated lung: 1 x 1 cm by chest x-ray or at least 2 cm in 1 dimension by CT scan Liver lesion, soft tissue mass, or lymph node: at least 2 cm in 1 dimension by CT scan or sonogram