A soil isolate named Streptomyces hofunensis sp. nov. was found to produce seldomycin factors 1, 2, 3 and 5, new aminoglycoside antibiotics. Taxonomy of the producing organism, a study of cultural conditions for seldomycin production, and antibacterial activity of seldomycins are reported. Seldomycin factor 5 was the most active both in vitro and in vivo against gram-positive and negative bacteria.