Philadelphia chromosome (Ph) - the characteristic chromosomal abnormality in hematopoietic stem cells causes chronic myeloid leukemia (CML). It develops during reciprocal translocation between long arms chromosomes 9 and 22. The translocation results in a fusion gene BCR-ABL which is responsible for synthesis of a constitutively activated tyrosine kinase. Cells carrying the translocations can be identified by several methods: cytogenetic analysis, FISH (Fluorescence In situ Hybridization) and RT-PCR (Reverse Transcriptase Polymerase Chain Reaction). One of the molecular methods uses to CML diagnostics there is also RQ-PCR (Real-time Quantitative PCR). It allows estimating very accurately the expression of the genes and application of molecular probe causes this method very specific and sensitive. Thanks to this technique there is the possibility to monitoring the therapy advance and minimal residual disease in CML patients. Up regulation of BCR-ABL gene, helps to detect the relapse even a few months before clinical signs of leukemia and modification of treatment. 60 patients with CML were qualified to the study group. All of them were cured in Hematology Department CMUJ in Krakow. Expression of BCR-ABL gene was measured for about three months. RQ-PCR method was performed by ABIPRISM 7700 using TaqMan technology. As a positive control uses to generate the standard curve plasmid dilutions were used. Differences between transcripts level during therapy were presented as a ratio of BCR-ABL to ABL copy number, and correlates to clinical image of the patients. The sensitivities of the tests were oscillated about 104 – 105. RQ-PCR method is very efficient and accurate assay to monitor BCR-ABL expression in CML patients treated with Imatinib and another tyrosine kinase inhibitors. RQ-PCR is reliable and sensitive method for monitoring CML patients after therapy. This is also convenient, robust and routine method for monitoring of minimal residual disease in CML patients. Quantifications of the level of residual disease using RQ-PCR has also therapeutic implications for the follow-up of therapeutic interventions for relapse.