The different binding of labeled lectins to the individual cell types of the normal mucosa indicates differences in glycoprotein composition of the: a) surface epithelial cells showing various degrees of differentiation; b) cell types lying above and below the generative cell zone; c) specific membrane systems of the parietal and chief cells. The enhanced peanut agglutinin (PNA) binding of activated, hyperplastic isthmus cells, of goblet cells in intestinal metaplasia, and even of the majority of gastric cancer cells may be indicative for their common origin and for their similar functional states in glycoprotein synthesis. Lectins demonstrate differences also in the mucus structure of the main types of gastric cancers. Adenocarcinomas show similar lectin binding patterns to activated isthmus cells, but the subtypes of signet ring cells resemble mucus neck cells or intestinal and colonic goblet cells, respectively. Glycoproteins which can be isolated by the lectins in a pure form allow further detailed studies in these fields.