The combination of CPT-11 with 5-fluorouracil (5-FU) in advanced colorectal cancer (ACC) represents an attractive approach. A phase II study was conducted to assess the tolerance and efficacy of CPT-11 in combination with leucovorin-modulated bolus plus infusional 5-FU given according to the de Gramont regimen in chemonaive patients with ACC. Fifty-four patients with histologically confirmed ACC were enrolled. The patients' median age was 65 years; 30 (55.5%) patients were men; performance status (World Health Organization) was 0 in 27 (50%) patients, 1 in 22 (41%), and 2 in 5 (9%). Patients received leucovorin (200 mg/m2/d) as a 2-hour intravenous infusion, followed by 5-FU as an intravenous bolus at 400 mg/m2/d, and then as a 22-hour continuous infusion at 600 mg/m2/d, repeated on 2 consecutive days. CPT-11 (180 mg/m2; 30-minute intravenous infusion) was administered on day 1, simultaneously with leucovorin administration. This cycle was repeated every 2 weeks. Complete response was achieved in 4 patients (8%) and partial response in 19 (37%) (overall response rate: 45%; 95% CI: 24-50.5%). Stable disease was achieved in 16 (31%) patients and progressive disease in 13 (25%). The median duration of response and the median TTP were 5 and 8 months, respectively. After a median follow-up period of 11 months, 33 (61%) patients are still alive; the median overall survival has not yet been reached. Thrombocytopenia and anemia were very rare. Grade III/IV neutropenia developed in 19 patients (36%); febrile neutropenia developed in 4 patients, and 1 of them died of sepsis. Grade IV diarrhea was seen in 7 (13%) patients, and 4 of them required hospitalization. Grade III and IV mucositis was observed in two (4%) and one (2%) patients, respectively. Other toxicities were mild. The combination of CPT-11 and bolus plus infusional 5-FU is a relatively well-tolerated and effective first-line treatment in ACC. Final results from large phase III trials are awaited to clarify whether the CPT-11/5-FU combinations should be considered as "standard" first-line treatment in ACC.