We have identified a number of gangliosides from human erythrocytes that have not previously been detected in these cells, including two new compounds. The gangliosides were separated into monosialo- and disialoganglioside fractions by DEAE-column chromatography. Two monosialogangliosides that have not been previously detected in these cells are GM2 and GM1. Two other monosialogangliosides have the same carbohydrate structure, NeuAc(alpha 2-3)Gal(beta 1-4)GlcNAc(beta 1-3)Gal(beta 1-4)GlcNAc(beta 1-3)Gal(beta 1-4) Glc-Cer, but they contain different fatty acids. The compound with higher chromatographic mobility (MG-5) contains a predominance of C22 and C24 fatty acids, whereas the principal fatty acid of the slower compound (MG-6) is C16. Both gangliosides are receptors for human anti-p and anti-Gd cold agglutinins. Six disialogangliosides not identifed previously in human red cells include GD3, GD1a, GD1b, DG-3, (formula: see text). The latter two are newly identified compounds and DG-4 contains a sugar sequence that has not been described previously, sialic acid residues linked to different hydroxyl groups of the same galactose.