Human secretory IgA (S-IgA) from colostrum contains 8.7% carbohydrate consisting of 0.7% fucose, 2.6% mannose, 1.6% galactose, 2.5% glucosamine, 0.2% galactosamine, and 1.1% sialic acid. The carbohydrate content is unevenly distributed among the polypeptide chains. Assuming that the S-IgA is composed of four heavy (H) chains, four light (L) chains, one secretory component (SC) and one J chain, the total carbohydrate content would be distributed as follows: 63% in H chains, 28% in SC, 6.5% in J chain, and 2.5% in L chains. The qualitative composition and the ratio between individual carbohydrates is similar in the different types of polypeptide chains, with the two following exceptions: galactosamine was found only in H chains and a higher content of fucose was detected in SC than in the rest of the chains.