The FMS-like tyrosine kinase-3 (FLT3), which belongs to the class III receptor tyrosine kinase family, expressed by immature hematopoietic cells, plays an important role in the proliferation, differentiation and survival of stem cells. The activating mutations of FLT3 gene have been reported to be of prognostic significance. The most common somatic alteration of the FLT3 gene is the Internal Tandem Duplication (FLT3/ITD), which is caused by the elongation of the juxtamembrane (JM) domain of FLT3. The duplicated fragment size varies from 3 to more than 400 base pair, always occurs in multiples of three while the reading frame is preserved. The elongated segment of DNA can be amplified by polymerase chain reaction (PCR), and the products are separated by gel electrophoresis. The FLT3/ITD is found in 20-40% of adult AML patients and is the most frequent mutation in leukemia. Using native peripheral blood and bone marrow from AML and non-AML patients (total of 19 samples), and samples from the RNA bank (total of eight samples), the authors purpose was to work out a method for FLT3/ITD detection, which can be used in routine diagnostics. All samples produced detectable PCR products, which proofs that this procedure can be used for the detection of FLT3/ITD mutations in daily clinical practice.