The primary objective of this study was to determine the maximum tolerable dose (MTD) and dose-limiting toxicity (DLT) for bolus 5-fluorouracil (5-FU) administered on a biweekly schedule and in combination with fixed doses of leucovorin (LV) and oxaliplatin. The secondary objectives were to evaluate the toxicity profile and antitumor activity of this regimen for pre-treated patients with advanced colorectal cancer. A total of 26 patients with documented fluoropyrimidine-resistant, advanced colorectal cancer were enrolled into this phase I study. Fixed dose of oxaliplatin (85 mg/m2) was delivered as an i.v. infusion over 2 h, followed by LV (20 mg/m2) and 5-FU bolus every 2 weeks. The starting dose of 5-FU was 600 mg/m2, which was then incremented by 100 mg/m2for each dose level. The DLT was determined for the first two treatment cycles, while toxicity and efficacy were evaluated throughout treatment. Six dose levels were tested. The MTD of 5-FU was deemed to be 1000 mg/m2since dose-limiting fatigue was noted for three of the five-patient cohort during the first two cycles of chemotherapy at dose level 6. The most frequent treatment-related toxicities during the study were neutropenia, vomiting, diarrhea, fatigue and neuropathy. In an intent-to-treat analysis, the objective response rate was 30.8% (95% confidence interval 11.8–49.8%) for the 26 patients. The combination of bolus 5-FU/LV and oxaliplatin every 2 weeks is a feasible and effective treatment at the recommended dosages. A phase II study, to more-precisely define activity and toxicity, is ongoing.