Interferon (IFN)-alpha, the molecule used in the treatment of chronic myelogenous leukemia and initially prepared from human leucocytes,is now produced essentially by recombinant techniques. Polyethylene glycol (PEG) modifications of proteins could be more effective than the regular molecules; thus, pegylated IFNs more recently have been tested in chronic myelogenous leukemia. PEG modification of proteins reduces sensitivity to proteolysis. Moreover,administration of pegylated IFNs results in less antigenicity and immunogenicity, and prolongation of their plasma half-life has been assessed by pharmacokinetic studies. It is assumed, therefore, that this compound could be more effective and better tolerated. Given the results recently obtained with imatinib, however, whether IFN-alpha will still have a therapeutic role is questionable.