A new diamino sugar, 3-amino-3-deoxy-alpha-D-altropyranosyl 3-amino-3-deoxy-alpha-D-altropyranoside (5) was synthesized by two routes starting from alpha,alpha-trehalose. The first route involved reduction and deprotection of a previously described, benzylidenated diazido analog. The second approach proceeded from the known 2,2'-di-O-benzyl-4,6;4',6'-bis-O-benzylidene derivative of alpha-D-altropyranosyl alpha-D-altropyranoside, to the corresponding 3,3'-diketone, which was subjected to reductive amination with sodium cyanoborohydride and ammonium acetate. The major product, separated in 39% yield from by-products after N-acetylation, was deprotected to give 5. Four by-products were isolated in low yields and determined to be monoaminated analogs which comprise two epimeric, 3'-hydroxy structures and two 3'-epimeric, 3'-cyano-3'-hydroxy structures in their non-aminated residues. A number of observations concerning the 13C- and 1H-n.m.r. spectra of the products are discussed, especially with regard to chemical-shift dependencies for certain ring and substituent protons, and attention is drawn to some inter-residue shielding phenomena.