As a single agent, irinotecan has demonstrated efficacy in metastatic 5FU resistant colorectal metastatic cancer. Chemotherapy with fluorouracil (5FU) plus leucovorin remains a standard in the treatment of patients with metastatic colorectal cancer. It seemed logical to test the combination of this reference treatment and the new agent. The first trials gave rather disappointing results, suggesting an inhibition of the metabolism of irinotecan into SN38 when 5FU was present in the circulation. More recent studies have given totally different results with a very good tolerance and strong efficacy of the combination of weekly folinic acid + 5FU and irinotecan or LV5FU2 (the so-called de Gramont regimen) and irinotecan. The results were so good that these new schedules are currently developed as first line regimen. Another way to combine 5FU, folinic acid and irinotecan is to alternate a cycle of 5FU, folinic acid and a cycle of irinotecan. Such an alternated schedule has given encouraging results with an objective response rate greater than 30% and a long median survival time (more than 16 months). It is also very easy to combine irinotecan with other drug which have demonstrated activity in the treatment of colorectal cancer. The combinations of irinotecan and mitomycin C or oxaliplatin have given very good results with high objective response rates and good tolerance. Irinotecan plays now an important part in the treatment of metastatic colorectal cancer. This part becomes larger due to the results of the combination trials already presented which have shown strong efficacy and good tolerance.