Inherited differences in xenobiotic transport and metabolism may play an important role in the development of adult acute myeloid leukemia (AML) and response to the chemotherapy. An ATP-binding cassette (ABC) family transporter P-glycoprotein (P-gp or ABCB1), encoded by ABCB1 (MDR1) gene, is involved in the protection against xenobiotics and multi-drug resistance. The aim of this study was to investigate the potential involvement of the ABCB1 gene exon 26 3435C>T single nucleotide polymorphism (SNP) in the genetic susceptibility to AML and regulation of P-gp expression and activity in AML cells. A total of 180 adult AML patients and 180 sex-matched controls were genotyped using PCR-RFLP method. Moreover, in 40 AML patients ABCB1 gene expression was studied by real-time RT-PCR and P-gp expression and activity were assessed by flow cytometry assays. The prevalence of 3435C>T ABCB1 polymorphism was similar in patient and control cohorts (P = 0.16). Furthermore, the carriers of different ABCB1 genotypes did not differ significantly according to ABCB1 gene expression (P = 0.99), P-gp expression (P = 0.42) and P-gp activity (P = 0.83) in leukemic cells. The authors conclude that isolated 3435C>T ABCB1 SNP is not a major factor of the genetic susceptibility to adult AML, and that genotyping of this polymorphism does not allow predicting P-gp expression or activity in AML cells.