From comparative investigations regarding the efficiency of introducing exogenous genes into cultured cells using DEAE-dextran and DEAE-dextran-MMA (methyl methacrylate ester) graft copolymer (2-diethylaminoethyl-dextranmethyl methacrylate graft copolymer; DDMC) as a nonviral carrier, we have confirmed that the gene transfection efficiency of DDMC is higher than that of DEAE-dextran. Comparative investigations in which DNA encoding luciferase (pGL3 control vector; Promega) was introduced into COS-7 cells derived from African green monkey kidney cells with and without the use of an incubator shaker were also carried out using various concentrations of DDMC. Without an incubator shaker, the transfection efficiency results were reversed, namely that the gene introduction efficiency of DDMC was inferior to that of DEAE-dextran. The aqueous solution of the cationic graft-copolymer displays thixotropic properties, which is why a strong shear stress is needed for it to flow and wet the cells. The reaction between DNA and DDMC is thought to be a Michaelis-Menten type complex formation reaction that can be described by the following equation: Complex amount = K1 (DNA concentration) (DDMC concentration).The complex formation reaction is thought to involve Coulomb forces between DDMC and DNA and is also significantly influenced by hydrogen bonding strength along with hydrophobic bonding strength due to the hydrophobicity of the grafted MMA sections.