Monitoring of chronic myeloid leukemia treatment efficacy requires very sensitive methods of BCR-ABL gene detection based on polymerase chain reaction (PCR). The lack of comparability of BCR-ABL mRNA quantification results generated by various methodologies in different laboratories was the cause of an international multicenter trial initiation with the participation of 133 laboratories in 24 European countries cooperating within the "EUTOS for CML" project. Pracownia Diagnostyki Molekularnej Kliniki Hematologii is taking part in standardisation rounds organised since 2005. The compatibility of methodology used in Pracownia with European Leukemia Net (ELN) standards was confirmed, and correction factor for the expression of RQ-PCR results in an international scale was calculated. Pracownia was charge by ELN with a task of conducting the standardisation in polish molecular biology laboratories. Test probes were prepared and sent to eight cooperating laboratories. The results obtained in six laboratories were concordant with results from laboratory in Krakow after conversion to international scale, therefore it was possible to calculate individual correction factors. The participation of polish laboratories in international standardization process created the opportunity for unification of BCR-ABL quantification methodologies with recommendations of international experts, and showed that the quality of analyses performed in majority of them was satisfactory enough to calculate correction factor and to express the RQ-PCR results in widely accepted international scale.