Tyrosine kinase inhibitors (TKIs) have dramatically improved the treatment of chronic myeloid leukemia (CML). However, resistances are occasionally observed, mainly due to mutations within the BCR-ABL kinase domain. The T315I substitution confers complete resistance to TKIs commonly used in clinical practice. In the present study, we used an allele-specific quantitative-RT-PCR to perform a molecular follow-up of BCR-ABL transcripts harboring the T315I mutation. We retrospectively quantified BCR-ABL315I mRNA in five patients who acquired the T315I mutation. Our results highlight the relevance of allele-specific Q-RT-PCR experiments for the monitoring of mutated BCR-ABL transcripts and suggest that the kinetics of emergence of T315I mutant mRNA is influenced by the stage of the disease and the presence of previous BCR-ABL kinase domain mutations.