Two novel linear polyene antibiotics, termed linearmycin A 1 and B 2, have been isolated from the mycelial extracts of Streptomyces sp. no. 30 and characterized as compounds 1 and 2, respectively. These compounds have similar, long linear structures terminating with amino and carboxylic acid groups, and show antifungal and antibacterial activity. The incorporation experiments using l3C-labe1led acetate and propionate suggest that 1 is biosynthesized from one y-aminobutyric acid, 24 acetate and 4 propionate molecules, by a polyketide pathway. In the course of our screening search for new antifungal agents, using a spheroplast regeneration system of Cundidu ulbicuns, mycelial extracts of Streptomyces sp. no. 30 were found to greatly inhibit the cell-wall regeneration process. This finding prompted us to isolate and characterize the active principle, which led to a discovery of novel linear polyene antibiotics, termed linearmycin A 1 and B 2. We have already reported the preliminary elucidation of the structure and biosynthesis of linearmycin A. In this paper, we describe the isolation, detailed structural elucidation and biosynthesis as well as antimicrobial activity of linearmycins.