Randomized studies have tested a variety of strategies to improve the activity of 5-fluorouracil (5-FU) in colorectal cancer patients. Results from 14 randomized trials comparing 5-FU administered via intravenous (i.v.) bolus either as a single agent or modulated by leucovorin indicate a significantly higher response rate with 5-FU/leucovorin (25% vs 13% of assessable patients). Sequential methotrexate followed by i.v. bolus 5-FU is associated with a higher response rate. Continuous infusion schedules also produce superior response rates compared to bolus 5-FU alone. Published meta-analyses indicate a small, but statistically significant, survival advantage for methotrexate/5-FU and infusional 5-FU, but not for leucovorin-modulated 5-FU. Although the incidence of hand-foot syndrome is higher with protracted infusional 5-FU, the incidence of other toxicities including myelosuppression, diarrhea, and mucositis is low. Oral administration of 5-FU may simulate infusional schedules while avoiding catheter-related complications.