Enteropathogenic Escherichia coli (EPEC) is a bacterial pathogen that causes diarrhea in infants by adhering to intestinal epithelial cells. EPEC induces host cell protein phosphorylation and increases intraceUular calcium levels that may function to initiate cytoskeletal rearrangement. We found that EPEC triggers the release of inositol phosphates (IPs) after adherence of bacteria to cultured epithelial cells. We also demonstrated that the EPEC-induced flux of IPs precedes actin rearrangement and bacterial invasion. EPEC mutants and tyrosine protein kinase inhibitors were used to establish that formation of IPs is dependent on tyrosine phosphorylation of a 90-kD HeLa protein. Collectively these results suggest that EPEC-induced tyrosine phosphorylation of a host cell substrate(s) leads to release of IPs, which may then trigger cytoskeletal rearrangement.