Novikoff ascites tumor cell homogenate was found to catalyze the transfer of [14C]N-acetylglucosamine from UDP-[14C]GlcNAc to asialo-alpha 1-acid glycoprotein. Mucins appeared to be poor acceptors. Methylation and hydrolysis of the product formed in an incubation with UDP-GlcNAc and asialo-alpha 1-acid [3H]glycoprotein yielded 2,4,6-trimethyl [3H]galactose and 2,3,4-trimethyl [3H]galactose, indicating that N-acetylglucosaminyl residues were introduced to position C-3 and C-6 of the terminal galactoses on the glycoprotein. It is concluded that Novikoff cells contain two N-acetylglucosaminyltransferases which might be involved in the synthesis of linear and branched forms of cell surface polylactosaminoglycans and blood group I/i antigenic structures.