In this report we describe the alteration of the N-linked oligosaccharide terminal sequences of Chinese hamster ovary cell glycoproteins by expression of a beta-galactoside alpha 2,6-sialyltransferase cDNA. While wild type cells normally produce sugar chains terminating in the NeuAc alpha 2,3Gal linkage, the expressed enzyme competes with the endogenous sialyltransferase to attach an alternative terminal sequence, NeuAc alpha 2,6Gal. Subcellular localization of the NeuAc alpha 2,6Gal product by lectin-gold electron microscopy revealed localization throughout the Golgi apparatus cis to trans, post-Golgi membranes and vesicular structures. The results demonstrate the potential for purposefully altering terminal carbohydrate structures in vivo by "mis-expressing" terminal glycosyltransferases that compete with the endogenous enzyme normally produced by the cells.