In order to analyze the glycosylation of a glycoprotein by FACE, oligosaccharides are released using PNG'ase F (N-Glycanase) and labelled with the fluorophore ANTS (8, aminonaphthalene-1,3,6-trisulfonate). Fluorescently labelled oligosaccharides are then separated by polyacrylamide gel electrophoresis and visualized by exposure to UV light. A digital image is acquired and the relative fluorescence of the oligosaccharide bands are determined. Recombinant human glucocerebrosidase (rGC) is produced in Chinese Hamster Ovary Cells. During the purification of this glycoprotein, the N-linked oligosaccharide chains are modified by enzymatic removal of terminal monosaccharides using neuraminidase, beta-galactosidase and beta-hexosaminidase. This modification alters the non-reducing ends of the oligosaccharide chains to produce forms where the majority of the terminal sugar residues are mannose. A FACE oligosaccharide profiling method was developed and validated to measure the efficiency of this oligosaccharide modification process. Strengths and weaknesses of FACE analysis for quantitative oligosaccharide analysis will be discussed.