Variable (Fv) domain N-glycosylation sites are found in approximately 20% of human immunoglobulin Gs (IgGs) in addition to the conserved N-glycosylation sites in the C(H)2 domains. The carbohydrate structures of the Fv glycans and their impact on in vivo half-life are not well characterized. Oligosaccharide structures in a humanized anti-Abeta IgG1 monoclonal antibody (Mab) with an N-glycosylation site in the complementary determining region (CDR2) of the heavy chain variable region were elucidated by LC/MS analysis following sequential exoglycosidase treatments of the endoproteinase Lys-C digest. Results showed that the major N-linked oligosaccharide structures in the Fv region have three characteristics (core-fucosylated biantennary oligosaccharides with one or two N-glycolylneuraminic acid [NeuGc] residues, zero or one alpha-linked Gal residue, and zero or one beta-linked GalNAc residue), whereas N-linked oligosaccharides in the Fc region contained typical Fc glycans (core-fucosylated, biantennary oligosaccharides with zero to two Gal residues). To elucidate the contribution of Fv glycans to the half-life of the antibody, a method that allows capture of the Mab and determination of its glycan structures at various time points after administration to mice was developed. Anti-Abeta antibody in mouse serum was immunocaptured by immobilized goat anti-human immunoglobulin Fc(gamma) antibody resin, and the captured material was treated with papain to generate Fab and Fc for LC/MS analysis. Different glycans in the Fc region showed the same clearance rate as demonstrated previously. In contrast to many other non-antibody glycosylated therapeutics, there is no strong correlation between oligosaccharide structures in the Fv region and their clearance rates in vivo. Our data indicated that biantennary oligosaccharides lacking galactosylation had slightly faster clearance rates than other structures in the Fv domain.