The strain Actinoplanes garbadinensis nov. sp. produces a peptide antibiotic, named gardimycin, which is active in vitro and in vivo against Gram-positive bacteria. Isolation and purification of the product have been accomplished by extraction from the broth with butanol and dialysis of the crude extract, followed by counter-current distribution. Gardimycin is an open chain peptide with an approximate minimal formula C84H138N18S3-4O34Na. The following amino acids have been identified by column chromatography of an acid hydrolysate: serine, glutamic acid, alanine, leucine, isoleucine, glycine, valine and two sulphur-containing amino acids whose structure is presently under study. Tryptophan has been identified in an alkaline hydrolysate.