A dose-intensive regimen of 5-fluorouracil for the treatment of metastatic colorectal carcinoma. 5-Fluorouracil (5-FU) was delivered in a dose-intensive schedule to 23 patients with metastatic or unresectable colorectal carcinoma. The schedule consisted of bolus single-dose 5-FU therapy 400 to 500 mg followed by 4-day infusion of 5-FU, 600 to 800 mg/m2/day, followed by a 17-day to 24-day infusion of 200 to 250 mg/m2/day. Partial remissions were seen in 22% of all eligible patients. Significant toxicity, including mucositis, diarrhea, and hand-foot syndrome, necessitated dose reductions in most patients. The authors conclude that 5-FU given in this moderately intensive schedule is associated with a moderate level of response, as easily achieved with more conventional schedules or with 5-FU-leucovorin combinations. Tumor responsiveness to dose intensive 5-FU regimens may be limited. 