Surfactin was found to consist of a mixture of two groups of homologous lipopeptides differing by their peptide sequence; Val7-surfactin was recently characterized as a minor companion of the previously described Leu7-surfactin. The addition of various α-amino acids to the culture media led to variations in the production ratios of the two congeners. The supplementation of l-valine or l-isoleucine to the culture medium resulted in a selective enhancement of the production of the Val7-surfactin whereas this production was very low when l-leucine was the nitrogen source in the culture medium.