Exposure of galactose-containing glycosphingolipids and certain glycoproteins to galactose oxidase followed by treatment with sodium borotritide was used to label specifically the terminal galactose and N-acetylgalactosamine moieties of these glycoconjugates. This labeling procedure was ineffective with a lipid isolated from rat testis, 1-O-palmityl-2-0-palmitoyl-3.beta.-galactosyl-glycerol, under conditions which resulted in excellent labeling of galactosyl-ceramide. Monogalactosyldiacylglycerol was also poorly labeled by this procedure. Neither 1-O-palmityl-2-O-palmitoyl-3.beta.-(3''-sulfogalactosyl)-glycerol nor sulfogalactosyl-ceramide (classical sulfatide) was labeled by this procedure indicating that sulfate substitution of the galactose inhibits the action of galactose oxidase. The labeling of galactosyl-ceramide was not inhibited in the presence of the galactoglycerolipid, sulfogalactoglycerolipid, or sulfatide. The property of the lipid aglycone responsible for inhibiting galactose oxidase action remains to be determined.