Immunohistochemical staining using a specific monoclonal antibody against sulfatide was performed to examine cellular localization of sulfatides in normal human gastric mucosa and in various types of gastric carcinoma. In normal gastric mucosa without Helicobacter pylori infection, both epithelial and glandular cells were densely stained with anti-sulfatide antibody. Sulfatide staining was more abundant in the apical area of normal epithelium compared with cytosol or basolateral areas. This tendency was stronger in the antrum than the gastric body and was more intensified in glandular cells of the pyloric glands. The levels of sulfatide expression were decreased in papillary and well-differentiated adenocarcinomas compared with normal mucosa, were markedly attenuated in moderately differentiated adenocarcinomas, and were very low in poorly differentiated adenocarcinomas. The polarity of the stains was preserved in gastric cancers that exhibited differentiated tissue organization. The levels of sulfatide expression were highly variable in signet ring carcinoma cells. The cancer cells that expressed sulfatides did not show any polarity of staining.