The products of nitrous acid deamination of per-O-methylated 2-amino-2dcoxy-D-glucitol and of 2-amino-2-deoxy-3-O-fl-r~-galactopyranosyl-D-glucitol and its per-O-methylated derivative have been characterized by g.l.c.-mass spectrometry after treatment with sodium borodeuteride and further substitution by acetylation, methylation, or (trideutcriomethyl)ation. The results confirm that the most important reaction pathway (1) involves a I ~2-hydride shift to give 2-deoxy-D-arabino-hexoses, but that significant side-reactions include (2) solvolytic displacement at C-2, (3) a 3~2-hydride shift, to give 2-deoxy-D-erythro-3-hexuloses, and ( 4) a C-4~C-2 migration to give 2-deoxy-2-C-(hydroxymcthyl)-D-ribosc and -D-arabinose. Reactions (3) and (4) result in elimination of the original 3-O-substituents, with the exposure of ncw reducing groups, from oligosaccharidcs terminated by 3-O-substituted 2amino-2-dcoxyhexitols. I NTRODUCTION Kochetkov et al. 2 have shown that 2-deoxyhexose-tcrminated oligosaccharidcs are formed on nitrous acid deamination of the corresponding oligosaccharides terminated by aminohexitol residues. Although 2-deoxy-D-arabhlo-hexose is the single most abundant product from the deamination of 2-amino-2-deoxy-D-glucitol, Bando and Matsushima 3 found that its formation is accompanied by that of smaller proportions of 2-deoxy-2-C-(hydroxymethyl)-o-ribose and -D-arabinose, 2-deoxy-Derythro-3-hexulose, and D-mannitol. The multiplicity of alternative reaction-pathways in the deamination of substituted aminohexitols was further suggested by the results of studies in this laboratory on the deamination of 2-amino-2-deoxy-D-galactitolterminated, oligosaccharide alditols formed, by reductive elimination followed by N-deacetylation, from O-glycosyl-substituted L-serine or L-threonine units in hoggastric mucin (unpublished results). Analysis of the products showed that dcamination *Amino-oligosaccharides. Part II. For Part I, see ref. 1.