The presence of BCR-ABL oncogene mutations in patients with chronic myeloid leukemia (CML) may be responsible for the failure of tyrosine kinase inhibitor (TKI) treatment. The aim of the study was to evaluate the frequency of BCR-ABL gene mutations in patients with CML treated with tyrosine kinase inhibitors. Our lab received 64 samples (34 women, 30 men) from patients with CML who failed or had suboptimal response to TKI treatment. The mutation analysis was performed in 61 patients with CML, 3 patients could not be tested because of inadequate RNA quality. An 866 base pair fragment containing the ABL kinase domain was amplified in a seminested RT (reverse transcriptase)-PCR and then sequenced using Applied Biosystems BigDye Terminator chemistry with two pairs of primers. We analyzed 61 patients with CML, 11 mutations were detected in 13 (21%) patients and SNP (single nucleotide polymorphism) in 6 patients (10%). In addition to 9 point mutations (G250E / F317L, F359V, L387M, Y253H, M388L, M244V, T315I, D276G), 35 bp insertion between exons 8 and 9 and deletion exon 7 were detected. Our results demonstrate that direct sequencing is suitable for routine clinical monitoring patients with CML and may be useful for optimizing therapy.