In the course of screening for new antibiotics active against anaerobic bacteria, a Streptomyces strain No. H230-5 that had been isolated from a soil sample collected in England was found to produce a new antibiotic. This agent, designated as Bu-2545, was active against anaerobic organisms as well as aerobic Gram-positive bacteria. Antibiotic Bu-2545 is structurally related to celesticetin and lincomycin, having structural units in common with these two antibiotics. This paper describes the producing organism, and the isolation, properties and structure of Bu-2545.