A 12-year-old female Basset Hound, weighing approximately 22 kg, had been vomiting fresh and hemolyzed blood intermittently for six weeks. Hemograms, serum chemistry determinations, urinalysis and fecal examinations were normal. Radiography showed some retention of barium in the esophagus and the cardiac region of the stomach. Vomiting of bloody gastric contents continued after several days of symptomatic treatment, and the dog was killed.Formalin-frxed tissues were processed routinely for light microscopy. One-millimeter cubes of formalin-fixed gastric mucosae were processed for electron microscopy. Plastic 1 -pm sections were stained with Paragon multiple stain (Ladd Research Industries, Burlington, Vt.) and appropriate areas were thin-sectioned. The rest of the tissue was processed routinely and examined by light microscopy. Thin sections were examined in an electron microscope. Deparaffmized sections 12 pm thick were prepared for scanning electron microscopy.Gross lesions were found only in the stomach. The cardia contained multiple linear and oblong zones of mucosal erosions and ulcerations, some with acute hemorrhages.Light microscopy showed many gastric mucosal defects extending to the muscularis mucosae. Large areas of acute hemorrhages were seen in and adjacent to the mucosal erosions and ulcerations. In some non-ulcerated parts of the gastric mucosa, the normal glandular architecture was distorted, and sometimes replaced by sheets of large histiocytes and a few multinucleated giant cells ( fig.