The composition and distribution of carbohydrates in the polypeptide chains of seven human IgA myeloma proteins were studied. It was found that 89-96 per cent of the carbohydrate was associated with the heavy (H) chains. Six of the immunoglobulins had similar carbohydrate compositions. Their H chains contained 0.3-0.6 residues of fucose, 4-5 of mannose, 5-6 of galactose, 4-5 of glucosamine, 2 of galactosamine, and 3-4 of sialic acid. One immunoglobulin lacked galactosamine, but had a higher carbohydrate content, and the relative proportions of the various monosaccharides present were different from those observed in the six immunoglobulins that contained this amino sugar. H chains of this IgA contained 3 residues of fucose, 13 of mannose, 3 of galactose, 12 of glucosamine and 1 of sialic acid. The preparations of light (L) chain contained small quantities of the same monosaccharides found in H chain with two exceptions; galactosamine was missing from all the L chain preparations and fucose was not found in two of them. The L chain preparations from dimeric immunoglobulins contained J chains, which were shown to contribute more than 50 per cent of the carbohydrates present in one of these preparations. © 1972.