Was studied by fluorescence spectroscopy methods of anticancer drugs doxorubicin interaction (DOX ) and paclitaxel ( PTX ) on the properties of the plasma membrane of cells of MCF- 7 breast adenocarcinoma . Used fluorescent probes TMA- DPH and Daud , allow the determination of external liquidity , the polar regions and the hydrophobic core of the lipid bilayer . It was found varying effects of both drugs . DOX and PTX influenced differently at the surface and the hydrophobic region of the membrane. Similar and DOX induced concentration-dependent changes in both areas of the lipid bilayer . Low concentrations of the drug resulted in membrane flux while a progressive increase in the concentration induced stiffening of the membrane. While PTX concentration independent affected mainly hydrophobic bilayer region causing it to stiffen . Equal concentrations of both drugs in varying degrees, changing the lipid bilayer fluidity . This may result from different PTX and DOX interaction with membrane components . PTX induced profound changes in membrane fluidity and at significantly lower concentrations than DOX , while exhibiting greater cytotoxicity to MCF- 7 cells . Quick , more than 70 % decrease in cell survival , accompanied by a significant decrease in membrane fluidity was observed for the same concentrations of PTX ( 0.01-1 mM ) . Similarly, the 60 % decrease in survival of MCF-7 cells and significant changes in plasma membrane fluidity - it liquefies or stiffening - observed for the same DOX concentrations ( 0.05-5 mM) . These results indicate that changes in membrane fluidity caused by DOX or PTX significantly interfere with cell proliferation, and suggested a possible correlation between the cytotoxicity of the study drugs , and the degree of membrane damage that they cause. The total effect of the combination of DOX and PTX on the membrane fluidity of MCF-7 cells was highly dependent on the concentration and the molar ratio of drug and significantly different from the effect of each of them used alone . There was no synergistic or additive effects of DOX and PTX on the plasma membrane fluidity of MCF- 7 cells . At certain concentrations of drugs were observed while their antagonist activity .