We report the results of a multicenter clinical trial comparing three combination chemotherapeutic regimens including 5-fluorouracil (5-FU) and l-leucovorin (l-LV). One hundred and twenty-two patients were randomized to three regimens comprising 5-FU (600 mg/m2) plus high-dose l-LV (250 mg/m2) in six doses given weekly by i.v. injection midway during a 2-hr infusion of l-LV (regimen A), 5-FU (370 mg/m2) plus high-dose l-LV (100 mg/m2) given simultaneously for 5 consecutive days and a 23-day interval between treatments (regimen B) and 5-FU (370 mg/m2) plus low-dose l-LV (10 mg/m2) with the same dose administration schedule as regimen B (regimen C). The response rates were 32.4% (12/37 cases) in Regimen A, 20.0% (8/40) in regimen B and 11.1% (4/36) in regimen C. The most prominent side effects observed in regimen A were diarrhea (53.8%) and leukopenia (53.8%); however, they were within permissible levels. The combinations of high-dose l-LV and 5-FU (regimen A and B) had higher response rates than that of low dose l-LV and 5-FU (regimen C). Weekly administration of high-dose l-LV and 5-FU (regimen A) is now being expanded to late phase II trials.