Boromycin is a boron-containing macrolide antibiotic that has been found in Streptomyces. Boromycin inhibits growth of B. subtilis (MIC = 0.05 µg/ml) and induces efflux of potassium ions from B. subtilis without affecting Na+/K+-ATPase activity. It decreases the synthesis of protein, RNA, and DNA in B. subtilis when used at a concentration of 0.05 µg/ml. It inhibits the growth of B. halodurans (MIC = 10 ng/ml) and inhibits the futalosine pathway of menaquinone synthesis in B. halodurans. Boromycin (3.4 nM) reverses bleomycin-induced cell cycle arrest at the G2 phase in Jurkat cells. It inhibits replication of the HIV-1 strains LAV-1 and RF and the HIV-2 strain LAV-2 in MT-4 cells (IC50s = 0.008, 0.11, and 0.007 µM, respectively). It also inhibits replication of a clinical isolate of HIV-1, strain KK-1, in MT-4 cells and peripheral blood mononuclear cells (PBMCs; IC50s = 0.14 and<0.1 µM, respectively).