Intimin is a bacterial outer membrane protein required for intimate attachment of enterohemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC) to mammalian cells. beta1-chain integrins have been proposed as candidate receptors for intimin. We found that binding of mammalian cells to immobilized intimin was not detectable unless mammalian cells were preinfected with EPEC or EHEC. beta1-chain integrin antagonists or inactivation of the gene encoding the beta1-chain did not affect binding of preinfected mammalian cells to intimin or the actin condensation associated with the attachment of EPEC. The results indicate that beta1-chain integrins are not essential for intimin-mediated cell attachment or EPEC-mediated actin polymerization.