Two different fixatives were applied to human gastric mucosa for the study of antigenic marker substances. The first consists of 96% ethanol and 1% acetic acid (EA method), the second of 4% formaldehyde, 0.5% picric acid and 0.25% glutaraldehyde (FPG method). Samples of resected gastric specimens were fixed, dehydrated and cleared in benzene and embedded in paraplast. The morphology of gastric tissue was well preserved by both methods and permitted the simultaneous application of classical staining procedures and the immunoenzyme peroxidase technique for the demonstration of gastric substances. The following marker substances could be demonstrated: Pepsinogen I and II group, surface epithelial antigen, parietal cell antigen, chief cell antigen, antral mucous cell antigen, carcinoembryonic antigen, goblet cell antigen and common site antigen of leucocytes. Various factors responsible for nonspecific reactions, such as endogenous peroxidase activity and protein-protein interactions were studied. The latter were circumvented by the use of highly purified antibodies or immunoglobulin fractions. The EA method proved to be the method of choice for future routine application of combined classical histology and immunoenzyme histology in gastric and intestinal diseases.