The study of the carbohydrates of human erythrocyte membranes has been mainly focused on their glycopeptidic and glycolipidic complexes. Modifications of these carbohydrates have been described in subjects with various pathological states. In order to characterize possible changes of the glycopeptides, or glycolipids obtained from erythrocyte membrane in various pathological situations, the determination of the carbohydrate content of the whole membrane appeared a necessary preliminary. This study concerns the determination of the normal values of the main carbohydrates of whole human erythrocyte membranes, with respect to their blood group. Erythrocyte membranes were prepared from donors of the four ABO blood groups. After acidic hydrolysis, the contents of fucose, mannose, galactose, glucose, glucosamine, galactosamine and N-acetylneuraminic acid in each blood group were determined and compared with one another. The galactosamine content of A, B and AB erythrocyte membranes is significantly higher than that of the O-erythrocyte. For galactose, the differences are significant for the following pairs: A/O; B/O; AB/O; A/B; A/AB. Significant differences in the mannose contents of O-erythrocytes and A, B and AB erythrocytes have also been found. This result suggests that a basic difference, in the core of the oligosaccharide chains, may exist between O and A, B, AB erythrocyte membranes.