BACKGROUND: A phase I multicentre trial was conducted to define the recommended dose of capecitabine in combination with oxaliplatin and irinotecan (OCX) in metastatic colorectal cancer. PATIENTS AND METHODS: Patients with performance status (PS) < 2 and adequate haematological, renal and liver function received oxaliplatin 70 mg/m(2) on days 1 and 15, irinotecan 100 mg/m(2) on days 8 and 22 and one of five dose levels (DL 1-5, between 800 and 1,600 mg/ m(2)) of capecitabine on days 1-29 every 5 weeks. RESULTS: 23 patients received a median of 3 cycles. 3 dose-limiting toxicities occurred (DL 1: grade 3 (G3) elevated alkaline phosphatase; DL 5: 1 patient G4 hyperglycaemia/G3 diarrhoea and 1 sudden death). The most common severe adverse event was G3 diarrhoea (13%). Severe haematotoxicity was rare. Therapy was stopped mainly due to metastasectomy or tumour progression (7 patients each). 8 patients reached a partial response. Median time to progression and overall survival (OS) were 8.0 and 21.9 months, respectively. CONCLUSIONS: The recommended capecitabine dose in this schedule is 1,400 mg/m(2) daily. The OCX regimen is well tolerated. The response rate was surprisingly low with progression-free survival (PFS) and OS within the range of a triple combination. Further studies in combination with targeted agents are warranted.