In Japan, cancer chemotherapy for advanced and recurrent colorectal cancer has not been adequately developed in comparison with the USA and Europe. However, the number of patients with advanced colorectal cancer has increased dramatically in this decade. Therefore, effective and feasible regimens against colorectal cancer are urgently needed. We designed a new regimen to evaluate the efficacy and feasibility of weekly low dose CPT-11 combined with 5-FU/l-LV therapy based on an RPMI regimen against advanced and recurrent colorectal cancer. Twenty patients were enrolled in this study. Weekly administration (CPT-11; 60 mg/m(2) div for 1st-line chemotherapy, 40 mg/m(2) div for 2nd-or 3rd-line chemotherapy, l-LV; 200 mg/m(2) div, 5-FU; 500 mg/m(2) iv, 3 consecutive weeks, 1-week break) was performed on an ambulatory basis. The treatment cycles were repeated every 4 weeks until disease progression and/or severe toxic events occurred. The overall response rate was 31.6% with 5.3% complete response and 26.3% partial response in addition to 42.1% with no changes beyond 3 months. These results suggested that the clinical benefit was shown in 73.7% of patients. Furthermore, median TTF (time to failure) of this regimen was 6.5 months and MST was 20.4 months, respectively. On the other hand, adverse events were restricted to grade 3 with 30.0% neutorocytopenia and 5.0% thrombocytopenia. Therefore, weekly low-dose CPT-11 combined with 5-FU/l-LV therapy seems to be extremely useful, with excellent anti-tumor effect and tolerable adverse reactions, for the treatment of advanced and recurrent colorectal cancer on an ambulatory basis.