The teichomycins are new antibiotics produced by Actinoplanes teichomyceticus nov. sp. Teichomycin A1 is a phosphorus-containing antibiotic, active in vitro and in vivo against gram-positive bacteria, and active only in vitro against gram-negative bacteria. Teichomycin A2 is a chlorine-containing antibiotic, active in vitro and in vivo against gram-positive bacteria. Isolation, purification and physical and chemical properties of the two antibiotics are reported. Teichomycin A1 is a member of the phosphoglycolipid class of antibiotics while teichomycin A2 is related to the group of the glycopeptide antibiotics.