Statistical analyses of the carbohydrate compositions of eleven IgA1 and six IgA2 meyloma proteins revealed that in addition to the known difference in the content of galactosamine, which is present only in proteins of IgA1 subclass, there are further quantitative differences in the carbohydrate composition of both subclasses. IgA2 immunoglobulins have significantly higher total carbohydrate content due to higher concentrations of fucose, mannose and glucosamine. No differences between the subclasses were found in the content of galactose and sialic acid. Certain relationships between monosaccharides in proteins of individual subclasses were established: in IgA1 the sialic acid content was found to be inversely correlated with fucose, in IgA2 a positive correlation was observed between galactose and sialic acid. © 1976.