A mouse monoclonal antibody ACFH18, produced by immunizing with human gastric cell line MKN-74, recognizes a novel glycolipid antigen, fucosyl-lactoneodecaosylceramide. In the present study, we investigated the immunohistological localization of this antigen and its biochemical detection in glycolipid fraction in normal and malignant human gastric tissue, compared with other tumor-associated type-2 chain glycolipid antigens such as sialyl Lex, sialyl Lex-i and Ley. Reactivity with ACFH18 was detected immunohistologically in the proliferation zone of normal fundic gland region as well as in 38 of 54 cases of gastric cancer, with preferential binding to undifferentiated type cancer. Glycolipids reacting with ACFH18, especially slow-migrating glycolipids on thin-layer chromatography, were accumulated in all of four cancer specimens compared with normal mucosa obtained from the same patients. Many glycolipids with sialyl Lex or sialyl Lex-i epitope were detected in normal mucosa and almost all of these glycolipids were accumulated in cancer specimens. Sialyl LeX-i antigen was increased more specifically in cancer than sialyl LeX was. A Ley antigenic glycolipid was considerably decreased in three of four cancer cases and increased in one case. From these results, glycolipid detected by ACFH18 appeared to be a tumor-associated antigen comparable to sialyl LeX and sialyl Lex-i antigens, but with a unique character as an undifferentiated-type tumor-associated antigen.