Background: There is a high prevalence of infection by Enterohemorrhagic Escherichia coli (EHEC) and patients with hemolytic uremic syndrome (HUS) in Argentina. Aim: To study cattle and pigs as a possible reservoir of EHEC in Argentina. Material and methods: One hundred two healthy animals (68 cattles and 31 pigs) from a livestock in Argentina, were studied. Stool samples were obtained with a rectal swab. The strains were identified by DNA hybridization with specific gene probes detecting Shiga-like toxin 1 and 2 (Stx1, Stx2), and hly gen related to fimbrial adhesin-associated plasmid. EHEC strains were serogrouped using comercial antisera. Results: EHEC was isolated from 30 out of 68 bovines cultures (44.1%) and from 25 out of 31 pigs (58.1%). Isolates carrying genes codifying both Stx1 and Sxt2, were observed in 50% of cattle and 63.9% of pigs. The gene which codifies for hemolysin (associated to fimbrial adhesin) was observed in about 41% of EHEC isolates. Strains belonging to serogroups O26, O111, and O157 were isolated from cattle, and O111, and O157 from pigs. Conclusions: The high percentage of EHEC in both cattle and pigs and the presence of human infection-associated serogroups, suggests that these animals are a reservoir of EHEC associated with disease in humans (Rev Méd Chile 2000; 128: 1335-41).