Monoclonal antibody KH2 (IgM) reactive with lactosyl ceramide and neolactotetraosyl ceramide was applied for the first time to the staining of human cancerous and noncancerous tissues which were fixed with formalin and embedded in paraffin. Digestive-tract cancers originating from stomach, colon, pancreas, gallbladder and bile duct were clearly stained. The staining intensity was especially strong in the apical portion and the intraluminal content of adenocarcinomas. In noncancerous tissues, it was of interest that gastric intestinal metaplasia and certain fetal tissues were stained. A part of the tubules of the kidney, pancreatic ductal cells, lung alveolar epithelial cells and polymorphonuclear leukocytes were stained in normal adult tissues in our study. Enhancement of the intensity of immunostaining by neuraminidase treatment indicated that most of the antigenic determinants should be sialylated and the antigenicity exposed after neuraminidase treatment in several kinds of cancerous and noncancerous tissues. These data suggest that the monoclonal antibody KH2 may be useful in the immunohistologic diagnosis of formalin-fixed human cancerous tissues.