The colonization ability of a representative epidemic strain of V. cholerae O139 Bengal was studied in the oral rabbit colonization model and the nature of colonization in the ileal and jejunal tissues was examined ultrastructurally. Results of the colonization study and ileal loop assay indicated that the strain proliferates and colonizes the small intestine of the rabbit mucosal surface. Further, the electronmicroscopic study revealed the disruptive effect of the strain on the apical membrane of the epithelial cells. The results of this study suggested that apart from colonization, invasion of the bacteria was important in the pathogenesis of V. cholerae O139 mediated infections.