Tegafur-uracil (UFT) plus leucovorin (LV, folinic acid) with alternating irinotecan and oxaliplatin were effective and well tolerated in patients with metastatic colorectal cancer (mCRC) in a phase I study. This study expanded the maximum tolerated dose group. Patients aged >or=18 years had histologically confirmed, inoperable, previously untreated, measurable mCRC. Patients received irinotecan 180 mg m(-2) on day 1, oxaliplatin 100 mg m(-2) on day 15 and UFT 250 mg m(-2) plus LV 90 mg on days 1-21 every 28 days. The phase I/II study comprised 45 patients, 29 at the maximum tolerated dose (MTD). The response rate in 38 evaluable patients was 63% (95% confidence interval (CI): 49-80). Median time to progression and overall survival were 8.7 months (95% CI: 7.9-10.4) and 16.8 months (95% CI: 9.6-25.3), respectively. In the MTD group, one patient had grade 3 leucopenia; one had grade 3 neutropaenia; three had grade 3 diarrhoea; and one had grade 3 neurotoxicity. No hand-foot syndrome grade >1 was seen. In total, 67% of eligible patients received second-line therapy. UFT plus LV with alternating irinotecan and oxaliplatin is an efficacious first-line treatment for mCRC, with minimal neurotoxicity and hand-foot syndrome.