 We plan to follow prospectively a cohort of CML patients in order to study their compliance to therapy,pharmacological levels of imatinib and the prevalence of side effects. We expect to be able to correlate the actual dose received, the pharmacological levels of drug in blood, with the change in the level of residual disease measured by QPCR at various time points. We also want to gain insight into the relationship between compliance to therapy and specific side effects and between compliance and duration of treatment. We will also assess the adherence to imatinib therapy after increases in the drug dose that are part of standard treatment. 