The O-glycosidically linked carbohydrate units of glycophorin derived from horse erythrocyte membrane were released as reduced oligosaccharides by alkaline borohydride treatment. One tetrasaccharide, two trisaccharides, and two disaccharides were purified by gel filtration and ion-exchange chromatography. Studies employing periodate oxidation, methylation analysis and gas-liquid chromatography-mass spectrometry revealed the following structures for these oligosaccharides; a tetrasaccharide; N-glycolylneuraminyl-(2 leads to 3)-D-galactopyranosyl-(1 leads to 3)-[N-glycolylneuraminyl-(2 leads to 6)]-D-N-acetylgalactosaminitol, trisaccharides; N-glycolylneuraminyl-(2 leads to 3)-D-galactopyranosyl-(1 leads to 3)-D-N-acetylgalactosaminitol and D-galactopyranosyl-(1 leads to 3)-[N-glycolylneuraminyl-(2 leads to 6)-a1-D-N-acetylgalactosaminitol, disaccharides; D-galactopyranosyl-(1 leads to 3)-D-N-acetylgalactosaminitol and N-glycolylneuraminyl-(2 leads to 3)-D-galacitol.