Alemtuzumab (Campath, MabCampath) is a humanized therapeutic monoclonal antibody (mAb) that recognizes the CD52 antigen expressed on normal and neoplastic lymphoid cells. This mAb is active in previously treated patients with B-cell chronic lymphocytic leukemia (B-CLL) refractory to alkylating agents and purine nucleoside analogs. Alemtuzumab is also investigated in previously untreated patients with this leukemia. The results of a prospective randomized Phase III study (CAM307 trial) comparing chlorambucil with alemtuzumab in the first-line treatment of progressive B-CLL were recently published. The overall response rate, complete remission rate, and progression-free survival were all superior for alemtuzumab. Moreover, elimination of minimal residual disease occurred in one third of complete responders to alemtuzumab and none to chlorambucil. Adverse events were similar in both arms with the exception of infusion-related reactions and cytomegalovirus infections. In 2001, alemtuzumab was approved in the USA and Europe as a third-line therapy for patients with B-CLL who had been treated with alkylating agents and failed fludarabine therapy. In September 2007, the US FDA, on the basis of CAM307 results, approved alemtuzumab for the treatment of previously untreated patients with B-CLL. Moreover, the European Commission recently granted marketing authorization to alemtuzumab for the treatment of patients with B-CLL for whom fludarabine combination monotherapy is not appropriate.