Objectives and background: The level of early MR is important for the optimization of therapy and making a decision to a switch to 2nd line therapy in patients (pts) who have not achieved an optimal response (OR). According to the recent recommendations at definition of OR on CML therapy, pts must have the level of BCR-ABL transcript gene at 10% or less and Ph-positive cells 35% or less at 3 months. But, in half of all cases of pts with BCR-ABL gt;10% at 3 months progression events happen between 3 and 6 months. The goal of our research was to investigate the prognostic impact of a large BCR-ABL transcript amount at 3 months on the subsequent response and the long-term outcome of CML pts treated frontline with IM.Methods: We have examined 185 pts, who have got IM from January 2010 up to the present. Molecular monitoring has been done regularly in all patients according to ELN recommendations. Median age was 49 years. All pts were in CP. BCR-ABL transcript levels were assessed by real-time quantitative PCR.Results: In our study 54% (100/185 cases) of pts achieved the optimal response with BCR-ABL transcript levels