Background/Aims: It has been suggested that the adhesion of H. pylori on the gastric epithelial cells are mediated by Bab A adhesin, Lewis antigen. However, precise mechanism of adhesion has not been elucidated yet. In this study, expression of different members of Rho-GTPases are investigated in the cultured AGS cells exposed to H. pylori by immunofluorescent staining and western blot analysis. Materials and Methods: AGS cell line was purchased from ATCC and cultured in DMEM with 10% FBS. Cultured cells were exposed to H. pylori at a density of O.D. of 1 at 600 nm for 1, 2 and 4 hrs. The cells were fixed in 4% paraformaldehyde. Fixed cells were washed and processed for immunofluorescence labeling. Primary antibodies against Rho, Rac1, and Cdc42 were labeled and visualized with FITC-labelled secondary antibody. Florescent labelled cells were observed with Zeiss Axioskop fluorescent microscope with appropriate filter sets. Proteins from the same cultured cells were extracted and examined by Western blot analysis. Results: Immunofluorescent labeling for Rho appeared as fine dots, which increased in size with the progress of adhesion. At 4 hr Rho-immunoreactivity was concentrated at the center of AGS cells. Rac1-immunoreactivity was present at the periphery and formed a reticulum on the top surface of AGS cells. Immunoreactivity for Cdc42 was not prominent. Western blot analysis confirmed the immunofluorescent labeling. Conclusions: These results showed the changes of different Rho-GTPases by H. pylori adhesion, and suggested that Rac1 was most important in the early interaction of H. pylori to the host cells. The exact mechanism for Rho-GTPases changes and the roles of different rho-GTPases in H. pylori pathophysiology need to be further investigated. (Korean J Helicobacter Res Prac 2002;2:148-155)