After a long period in which the only therapeutic approach for the management of colorectal cancer was the optimization of fluoropyrimidine-based chemotherapy, the last few years have seen the emergence of newly active chemotherapeutic agents endowed with novel mechanisms of action, such as oxaliplatin (OHP), irinotecan (CPT11), raltitrexed and oral 5-fluorouracil (5-FU) pro-drugs which can offer new therapeutic possibilities. The availability of these different classes of cytotoxic agents has introduced the possibility of combination chemotherapy. The most widely studied combinations are 5-FU/folinic acid (FA)/CPT11 and 5-FU/FA/OHP, both of which have been tested in two randomized studies. These trials consistently demonstrated that the addition of CPT11 or OHP to widely accepted infusional/bolus 5-FU/FA regimens is superior to the same 5-FU/FA schedule alone in term of response rate (rate of about > 50%) and time to progression. It's worth nothing that both trials with the combination of 5-FU/FA/CPT11 showed a significant survival benefit. Toxicity profiles were more pronounced with the combination therapies but the quality of life evaluation showed that the combinations had no negative impact on the evolution of the global health status over time. A current ongoing randomized study compares 5-FU/FA/CPT11 with 5-FU/FA/OHP in order to identify the best first-line chemotherapy. Preliminary results in terms of objective response and toxicity are similar for both treatments. Raltitrexed is a thymidilate synthase inhibitor with activity comparable to 5-FU and a convenient administration schedule. In our institution, we performed a phase II single center trial to assess the efficacy of the combination of raltitrexed and CPT11. The principal aim of the study was the overall response rate. We observed a very promising 51% overall response rate. Most relevant side effects were diarrhea in about 20% of patients, asthenia and vomiting. Two recent studies have assessed the efficacy and tolerability of raltitrexed-OHP combination therapy. The results showed that the combination is active (ORR: 46-62%) and tolerable. Promising results have also been obtained in phase I studies with the OHP/CPT11 combination. All these data need to be confirmed in phase II-III clinical trials. In conclusion, combination therapy with CPT11 plus 5-FU/FA produces a 2-3 month survival advantage over 5-FU/FA alone and represents the new reference in the first-line chemotherapy of colorectal cancer. The association of 5-FU/FA and OHP improves response rates and progression-free survival. The increase in toxicity of these combinations is predictable and reversible and does not compromise quality of life. These important data suggest that there is now a limited role for single-agent first-line chemotherapy of metastatic colorectal cancer.