1-Deamidino-, 3-deamidino- and 1,3-di(deamidino)dihydrostreptomycin (1, 2, 3) were prepared by treatment of dihydrostreptomycin (DHSM) with ammonia at 100 degrees C. The 3-guanidino group of DHSM is suggested to be more important than the 1-guanidino group for the antibacterial activity of DHSM. 1-N-[(S)-4-Amino-2-hydroxybutyryl) and 1-N-[(S)-4-guanidino-2-hydroxybutyryl] derivatives (4, 6) of 1-deamidinodihydrostreptomycin were futher prepared.