5-Epi-azido- and 5-epi-amino-4,6-di-O-(aminoglycosyl)-2,5-dideoxystreptamines and 1-N-alkyl derivatives thereof, valuable as antibacterial agents, are prepared from the corresponding 5-O-hydrocarbonsulfonyl (or substituted hydrocarbonsulfonyl)-4,6-di-O-(aminoglycosyl)-2-deoxystreptamine wherein all other hydroxyl functions and all amino functions are protected, by the reaction thereof with an alkali metal azide in an organic solvent followed by the reaction of the resulting 5-epi-azido-4,6-di-O-(aminoglycosyl)-2,5-dideoxystreptamine with base to remove the protecting groups, or with hydrogen in the presence of a catalyst or with an alkali metal in liquid ammonia, and thence cleavage of any remaining hydroxyl and amino protecting groups in the thereby formed 5-epi-amino-4,6-di-O-(aminoglycosyl)-2,5-dideoxystreptamine or 1-N-alkyl derivative thereof.In addition to the foregoing, methods are described whereby the 1-N-alkyl-5-epi-azido and 1-N-alkyl-5-epi-amino-4,6-di-O-(aminoglycosyl)-2,5-dideoxystreptamines are prepared from the corresponding 1-N-unsubstituted-5-epi-azido and 1-N-unsubstituted-5-epi-amino-4,6-di-O-(aminoglycosyl)-2,5-dideoxystreptamines.Pharmaceutical compositions comprising 5-epi-amino-4,6-di-O-(aminoglycosyl)-2,5-dideoxystreptamines, 1-N-alkyl-5-epi-amino-4,6-di-O-(aminoglycosyl)-2,5-dideoxystreptamines, 5-epi-azido-4,6-di-O-(aminoglycosyl)-2,5-dideoxystreptamines and 1-N-alkyl-5-epi-azido-4,6-di-O-(aminoglycosyl)-2,5-dideoxystreptamines elicit an antibacterial response in a warm blooded animal having a susceptible bacterial infection.