Mucins of the normal and malignant stomach and colon. The mucin composition of the normal human stomach and colon and in carcinomas derived from the stomach and colon has been investigated by gel filtration and a specific antibody to gastric mucin, by histochemical staining with the alcian blue/periodic acid-Schiff-positive reaction, and by gel electrophoresis and blotting to nitrocellulose. The gastric mucin is composed of high-molecular-weight glycoprotein components, ranging from 2.5 to 5 X 10(6) daltons, and a large proportion of a low-molecular-weight component, 50,000 daltons in weight. In contrast, the colon has a large high-molecular-weight component that is not found in the stomach. The mucin content is much higher in goblet cells and in the epithelium of the pit region of the stomach than in the surface epithelium, but it is low in colon carcinomas. Carcinomas from the stomach do not always possess goblet cells and the mucin content of some of these carcinomas is high, particularly in adenocarcinoma. The colon carcinomas have goblet cells and have a high content of mucin. The colon mucin of the normal human colon has similar chromatographic behavior and isoelectric properties to the gastric mucin. The colorectal carcinomas and the colonic carcinoma-derived cell lines have a very high content of gastric-type mucin, but contain also goblet cells and sulphated mucins. The carcinomas from the stomach have a very high content of sulphated mucins. The carcinomas derived from both parts of the gut have mucin that is not derived from the epithelial layer and may therefore be produced by the submucous glands, as well as goblet cells. The results of this study suggest that different regions of the gut may produce different types of mucin. The gastric mucin may have a protective function for the epithelium, and its absence may make it easier for a carcinoma to develop. The high content of sulphated mucins may have a similar protective effect. The mucin from the surface epithelium and the lower parts of the colon may be important in protecting the mucosal barrier, and its absence may be an important step in cancer development. The colon mucin may have an important protective function in the colon. The colorectal carcinoma-derived cells have a high proportion of gastric-type mucin, suggesting that they may be derived from the normal epithelium.