Abstract: The fluidity of membrane lipid regions of Plasmodium berghei- or Plasmodium yoelii- infected red blood cells has been determined by the fluorescence polarization technique using 1, 6-diphenyl-1, 3, 5-hexatriene (DPH) as a probe. The results showed that the fluidity of Plasmodium(berghei or yoelii)-infected red blood cell membranes was increased significantly as compared with that of normal controls judging from the degree of polarization and the microviscosity. Its mechanism was discussed briefly.