Salmonella typhimurium induced massive uptake of extracellular fluid in epithelial cells in the form of macropinosomes. The appearance of macropinosomes in the infected cell was related to the induction of membrane ruffling during bacterial invasion. A noninvasive S. typhimurium invA mutant did not trigger such effects in the host cell. Similarly, S. typhimurium invA mutants that invaded via the invasin protein from Yersinia pseudotuberculosis or adhered to the host cell via the afimbrial AFA-I adhesin from Escherichia coli did not trigger formation of macropinosomes. In contrast to the formation of macropinosomes in macrophages, the appearance of macropinosomes in S. typhimurium-infected epithelial cells did not require microtubules. These data suggest that massive uptake of extracellular fluid in S. typhimurium-infected epithelial cells is an event related to the invasion mechanisms used by this pathogen.