In this study, dielectric characterization of multidrug resistant (MDR) K562 human leukemia cells was carried out using a MEMS based electrorotation (ER) device with 3D electrodes. P-glycoprotein (P-gp) dependent MDR causes variation in cell dielectric properties (cell interior conductivity (sigma(i)), membrane capacitance (C-m) and total effective membrane conductance (G(m)*)) due to overexpression of P-gp, which modulates the activity of membrane-bound Cl- channels. Different cell populations resistant to varying levels of doxorubicin (DOX, 0.1-0.5 mu M) and imatinib (IMA, 0.2-0.5 mu M) were studied to reveal the relationship between cell dielectric properties and the degree of drug resistance. ER characterization results proved considerable changes in cell membrane and interior dielectric properties as the resistance level to chemotherapeutic drugs changes. The membrane dielectric properties of the cells increase significantly at low (0.1-0.2 mu M) drug resistance levels (K562/IMA-0.2: C-m = 15.63 +/- 3.02 mF m(-2) and G(m)* = 2953 +/- 82 S m(-2), and K562/DOX-0.1: C-m = 12.29 +/- 2.15 mF m(-2) and G(m)* = 1810 +/- 14 S m(-2)), compared to the sensitive ones (C-m = 8.93 +/- 1.43 mF m(-2) and G(m)* = 336 +/- 73 S m(-2)). However, they follow a decreasing trend as the drug resistance level increases (0.3-0.5 mu M). The membrane capacitance and effective conductance for IMA resistant K562 cells falls to 8.10 +/- 1.69 mF m(-2) and 113 +/- 18 S m(-2) in 0.5 mu M resistant cells, respectively. Similarly, the membrane capacitance and effective conductance of DOX resistant cells falls to 8.70 +/- 1.71 mF m(-2) and 1377 +/- 22 S m(-2) in 0.5 mu M resistant cells, respectively. However, no direct relationship could be observed between increased drug resistance and cell interior conductivity, which showed an oscillating behavior. Results prove that the degree of drug resistance significantly affects the dielectric properties of K562 cells, although they possess a similar size and morphology. Variations in cell dielectric properties result in differences in DEP crossover frequencies, which could be utilized in the detection and separation of MDR using dielectrophoretic based devices.