Sixty % of CML patients treated by Imatinib mesylate achieved a major cytogenetic responses (CCR) at 18 months. So, 40% of the patients must receive additional treatment. In vitro, it has been shown that IM and Interféron-alpha have synergic anti-proliferative effect on chromosome Ph+ cell lines. By using Peg-Interféron and IM combination, we hope to increase the cytogenetic response of patients.