A tetrasaccharide consisting of D-galactose, N-acetylneuraminic acid, N-acetylglucosamine and N-acetylgalactosaminitol (1 : 1 : 1: 1) was obtained from bovine colostrum kappa-casein. It is the main carbohydrate portion of a caseinoglycopeptide formed by alkaline borohydride treatment. The carbohydrate sequence was analyzed by enzymatic and chemical methods and by mass spectrometry, and was shown to be N-acetylglucosaminyl-beta-1-3-galactosyl-beta-1-3[N-acetylneuraminyl-alpha-2-6- ]-N-acetylgalactosaminitol.