Many current problems in immunology depend on a detailed understanding of oligosaccharide and glycoconjugate structures. In contrast to other biopolymers, oligosaccharides do not have well established and sensitive analytical procedures for the determination of their structures. Additionally, oligosaccharides because of branching, linkage, and structural isomerism, pose specific complications unique to this biopolymer. We have discussed MS data utilizing DCI and FAB ionization and presented new information that indicates FAB-MS can provide a wealth of structural information including sequence, branching and molecular weight. In the final sections FAB ionization and collision induced dissociation, have been discussed, two adjunct techniques that amplify the analytical value of MS instrumentation in the pursuit of oligosaccharide structure.