Oxaliplatin (L-OHP), irinotecan (CPT-11) and 5-fluorouracil (5-FU) have shown their efficacy in metastatic colorectal cancer. The synergism of these drugs has been demonstrated in vivo and in vitro. The aim of this study was to determine the recommended dose of the triple combination of L-OHP, CPT-11 and CI 5-FU for a further phase II study. Eighteen patients received the study treatment in four dose levels. The male:female ratio was 15:3 and the median age was 51.6 years (range 30-71). The type of tumor was colon in eight patients, rectum in four and other locations in six patients. The treatment was repeated every 2 weeks, at the fixed dose of L-OHP, 85 mg/m, and escalated doses of CPT-11 and 48-h infusion 5-FU of 100/2000, 100/2250, 125/2250 and 150/2250 mg/m. Only one previous treatment for the advanced disease was permitted. Patients received a median of 8 cycles (range 1-26) and a total of 152 cycles were administered. Dose intensity administered at dose level L-OHP 85 mg/m, CPT-11 150 mg/m and 5-FU 2250 mg/m was 95, 92 and 95% for L-OHP, CPT-11 and 5-FU, respectively. One patient in level 2 and one patient in level 4 presented dose-limiting toxicity that was not confirmed in the three required additional patients by level. The anti-tumor activity was assessed in nine patients: seven partial responses, one stable disease and one progressive disease. The maximum-tolerated dose was not reached, and thus the recommended dose for this combination schedule is L-OHP, 85 mg/m, CPT-11, 150 mg/m and 5-FU, 2250 mg/m 48-h continuous infusion, the same doses that were recommended for the drugs when administered in combination therapy of L-OHP + 5-FU or CPT-11 + 5-FU. A phase II study in first-line treatment of patients with metastatic colorectal cancer with this dose regimen is ongoing.