Metastatic colorectal cancer is very common in the Western hemisphere and current treatment modalities are not effective. In this study a prolonged (150-minute) infusion of gemcitabine at a constant dose rate of 10 mg/m2/min administered weekly for 3 consecutive weeks repeated every 4 weeks revealed a response rate of 4% (90% CI < 1%-18%). There were no complete responses. Treatment with gemcitabine produced moderate to severe toxicity as grade 3-4 neutropenia requiring dose modification was seen in 40% of patients treated. When used in this dose and schedule, gemcitabine does not appear to be effective for patients with metastatic colorectal cancer.