Most large proteins derived from animals have attached carbohydrate structures (glycans) that are added as a post-translational modification. At one time these glycans were thought to be unimportant to glycoprotein activity. However, now it is clear that an understanding of the carbohydrate component (glycan) of a recombinant glycoprotein is of importance for two main reasons. Firstly, the carbohydrate structures attached to a protein can affect many of its properties. This includes its pharmacokinetics, bioactivity, secretion, in vivo clearance, solubility, recognition and antigenicity, all of which influence the overall therapeutic profile of the glycoprotein. Secondly, quantitative and qualitative aspects of glycosylation can be affected by the production process in culture, including the host cell line, method of culture, extracellular environment and the protein itself (Jenkins and Curling, 1994).