A high-molecular-weight glycoprotein has been purified from the cervical mucus of the bonnet monkey (Macaca radiata). The glycoprotein was shown to be homogeneous by electrophoresis, sedimentation equilibrium, and N-terminal group determination, and to contain 19% protein, 19% D-galactose, 18% N-acetyl-D-galactosamine, 15% N-acetyl-D-glucosamine, 11% L-fucose, 10% sialic acid, and 1% sulfate groups, corresponding to about 1800 amino acid residues and 400 carbohydrate side chains of about 9 monosaccharides. The carbohydrate chains are linked to the peptide backbone through N-acetyl-D-galactosamine and serine (or threonine) residues. Reduction with dithiothreitol and alkylation with iodoacetic acid reduced the molecular mass from 1 to 0.5 X 10(6) daltons and produced subunits having the same size, charge, and N-terminal amino acid. Electrophoretic studies suggested the presence of disulfide bonds between two chains of the glycoprotein. Degradation with alkaline borohydride gave, after fractionation on Bio-Gel P-2, fractions containing L-fucose, D-galactose, N-acetyl-D-galactosaminitol, N-acetyl-D-galactosamine, N-acetyl-D-glucosamine, and sialic acid in the ratio of 1.0:3.0:1.0:1.0:1.3:1.0. Further fractionation by electrophoresis and paper chromatography gave a charged fraction representing 13% of the original glycoprotein. Enzymic degradation and methylation studies indicated the presence of the structure alpha-Gal-(1 leads to 3)-[Fuc(1 leads to 2)]-Gal-(1 leads to 4)-GlcNAc, linked to a core component containing N-acetyl-D-galactosaminitol.