In order to examine the effect of complex 2 in P-gp activity in our taxol-resistant cancer cells, including MCF-7, HCT-8 and A549, Rhodamine 123 (Rho123) exclusion assay and flow cytometric analysis were used to investigate the accumulation of the Rho123 dye in these cells after complex 2 treatment. This evidence concerns the gene PGP and cancer.