Acquired resistance to tyrosine kinase inhibitors (TKIs) in the treatment of chronic myelogenous leukemia (CML) is frequently caused by point mutations in the ABL kinase domain of the BCR-ABL fusion gene. The T315I mutation is the most common mutation found in the kinase domain and leads to complete resistance to existing TKIs. Sensitive and specific approaches for detecting this mutation in patient specimens can provide valuable information to guide treatment decisions and monitor their effectiveness. Here, we describe an allele-specific real-time polymerase chain reaction method to distinguish and quantify wild type or T315I mutant ABL transcripts. This approach has high specificity in identifying mutant transcripts and shows minimal interference from wild-type transcripts. As few as 5 copies of the T315I mutant transcript or 0.025% (2.5×10(-4)) T315I mutant transcripts could be detected by this method. This approach requires no additional specialized reagents other than those used in standard real-time polymerase chain reaction and therefore may be easily incorporated as an effective strategy for the early detection and monitoring of TKI resistance in patients with CML.