Chronic myeloid leukemia (CML) is a hemopoietic condition caused by chromosomal translocation t(9;22)(q34;q11) or bcr-abl fusion gene. The predominant variants of bcr-abl oncogene rearrangement are b3a2 and b2a2. The present study evaluated the efficacy of interferon-a therapy of CML patients and molecular prognostic factors. Cytogenetic response and complete hematological remission were more frequent in CML b3a2 treatment with interferon-a. Moreover, after therapy, chronic phase lasted in that group (p = 0.026) much longer. Overall survival in the group was significantly longer, too (p = 0.046).