Tetracenomycins B₃ and D₃, besides tetracenomycin D (D₁), were produced by a blocked mutant of the elloramycin producer Streptomyces olivaceus TÜ 2353. The compounds were isolated as red powders, and their structures were elucidated by comparing their physicochemical data with those of the known tetracenomycins A₂, B₁, B₂, D and E. Tetracenomycin B₃ (2), the main compound, and tetracenomycin D (3) were antibiotically inactive against Gram-positive and Gram-negative bacteria, whereas tetracenomycin D₃ (1) showed a moderate activity against Bacillus subtilis and Arthrobacter aurescens. Tetracenomycin B₃ (2) is the key intermediate where the biosynthesis of the elloramycins branches off from the line leading to tetracenomycin C (5) as the final product of the tetracenomycin biosynthesis branch.