Epoxide ring opening reactions of methyl 2,3-anhydro-4-azido-4-deoxy-pentopyranosides with hydroxide ion and methoxide ion are described. The products obtained by reactions of the epoxides with hydroxide ion are related, by preparation of their 2,3-di-O-methanesulfonyl derivatives, to known compounds or their enantiomers. Opening of the α-d(and l)-ribo epoxides with methoxide ion gave monomethylated products which were characterized by nuclear magnetic resonance analysis of their acetates. The relative yields of the two major products obtained in each case are not accounted for, in some cases, by consideration of only steric and inductive effects.