The morphological features of early intestinal ulcerations induced in rodents with axenic cultures of Entamoeba histolytica were studied by scanning and transmission electron microscopy. Amebas did not attach to the luminal surface of the mucosa except at interglandular regions, where parasites penetrated apparently through pseudopodial movement. Once in the lamina propria, trophozoites multiplied and destroyed mucosal components. Damage extended laterally through the mucosa, but progression to deeper layers of the intestinal wall was prevented by the muscularis mucosae, which acted as a partial barrier. This was eventually breached at focal points where amebas invaded the submucosa. Electron microscopy clearly showed the lysis of abundant polymorphonuclear neutrophil leukocytes (PMNs) by the amebas at the periphery of intestinal ulcerations as well as the lack of bacteria at these sites. This study demonstrates that recruitment and destruction of inflammatory cells following intestinal amebic invasion may take place in the absence of bacterial multiplication. The observations provide histological support to the hypothesis that lysis of PMNs by trophozoites participates in the genesis of amebic intestinal lesions.