Gel chromatography on Sephadex G150 or Bio-gel P150 resolved the gastric secretions into three fractions. The non-retarded fraction contained 70–90% of the total carbohydrate eluted in the three fractions. The gastric secretions before gel filtration and the non-retarded fraction contained the same carbohydrate residues and the three carbohydrate components, galactose, glucosamine and galactosamine, in the same quantitative proportions. The amino-acid composition of the non-retarded fraction showed marked similarities and characteristic quantitative relationships. Threonine and serine were found to constitute 45–50% of the total aminoacid content. The analytical data, ultracentrifugation and light scattering studies suggest that the non-retarded fraction is composed of macromolecules which have a common basic composition but which are polydisperse with reference to their charged end groups, fucose and size.