The aim of the study was to investigate the possibility of dual modulation of UFT with leucovorin and hydroxyurea in a phase II trial of metastatic colorectal cancer. A total of 77 patients with measurable disease were included. UFT (300 mg/m2) was given with a fixed dose of 1-leucovorin (22.5 mg daily) and hydroxyurea (0.5 g daily) for 28 days followed by a 7 days' rest period. Treatment continued until progression or unacceptable toxicity. Sixty-three patients were evaluable for response. One patient (1.6%) had a complete remission and 13 (20.6%) a partial response for an overall response rate of 22.2%. The treatment was well tolerated. No significant bone marrow depression occurred. Grade 2 gastrointestinal toxicity was recorded in 28.5% of the patients, and grade 3 in 12.9%. The median time to progression was 6.8 months and the median crude survival was 11 months. In conclusion, hydroxyurea did not appear to increase either the response rate or the toxicity. Phase III trials along the same line cannot be recommended.