There is the case report of 63-years old patient with Ph1 positive chronic myeloid leukaemia (CML) who is treated with 400 mg of imatinib daily. It is because of the secondary cytogenetic resistance to interferon alpha after two years from diagnosis. After initial cytogenetic response (10 % Bcr/Abl positive cells detected by bone marrow interphase FISH examination after 3 months and 1 log decrease in quantitative RT-PCR after 6month of treatment) there is the cytogenetic progression in one year with failure of the response to the escalated dosage 800 mg daily. It leads to the suspicion of imatinib resistance. In vitro tests confirm it: there is a high expression of WT1 gene, the presence of phosphorylated CRKL and detection of T315I mutation in Abl kinase domain. This article is aimed at detection of imatinib resistance in case of suspicion and should also show the review of the new treatment modalities. The resistance detection is important from clinical point of view. It allows to stop the therapy which is not useful and economically demanding, on the other side it moves it to the application of the new tyrosine kinase inhibitors, allogenic stem cell transplantation or to experimental treatment.

        Key words: Bcr/Abl fusion gene, WT1 gene, quantitative RT-PCR, tyrosine kinase inhibitors, T315I mutation