Enteroaggregative E. coil (EAEC) is an important aethiological causal agent of diarrhea in people of developed and undeveloped countries. Different in vitro and in vivo models have been proposed to study the pathdgenic and immune mechanisms of EAEC infaction. The aim of this study was to analyze whether BALB/c mice could be used as an animal model to study EAEC pathogenesis Six-week-old BALB/c mice were inoculated with EAEC strain 042 (044:H88) nalidixic acid resistant, and re-inoc-ulated ten days after. Mice feces were monitored for the presence of the EAEC strain over a period of 20 days . Bacteria were enumerated on MacConkey agar containing 100$mu$g of nalidixic acid per ml. Results showed that 35% of the animals were colonized for 3 days, 15% for 5 and 10% for more than 7 days . After re-inoculation only 16% of the animals remained colonized for more than 3 days. During the necropsy, the intestinal fluid of same of the infected animals presented mucus and blood. Six of these fluids showed the presence of IgA antibodies againset Pet toxin and IgG natibodies raised against the toxin were also detected in the animal serum. Histopathologic evidence confirms the stimulation of mucus hypersecretion, an increased amount of goblet cells and the presence of bacterial aggregates in the apical surfaces of intestinal epithelial cells. Edema was present in the submucosa. These results suggest that BALB/c mice could be used as an animal model for in vivo study of EAEC infection.