IgA antibodies reacting to enteropathogenic Escherichia coli (EPEC) antigens in human colostrum and their role in the inhibition of EPEC adherence to HEp-2 cells were studied. Colostrum IgA was isolated with a Sepharose anti-IgA column. IgA-depleted colostrum lost its inhibitory effect on EPEC adhesion, while the IgA-enriched eluate was a potent adherence inhibitor. The same eluate showed a significant loss of inhibitory activity after absorption with an EPEC strain showing localised adherence (LA+), but no alteration after absorption with an LA- strain. No bands were observed in Western blot analysis with LA+ absorbed eluate and with a crude extract of the EPEC strain, but the eluate absorbed with LA- showed a strong recognition of a 94-kDa band, a molecular weight equivalent to that of intimin. Colostrum antibodies reacting to non-protein antigens were not detected by Western blot analysis. The persistence of anti-EPEC IgA in the gastrointestinal tract was shown by the strong reactivity to the 94-kDa band in Western blot analysis of one mother's colostrum and her infant's faeces. These data confirm the role of colostrum antibodies in protecting the neonate against infections due to EPEC.