Poly(epsilon-l-lysine) (epsilon-PL) is a naturally-occurring l-lysine homopolymer having antimicrobial activity. A newly-isolated strain of Streptomyces aureofaciens produced a short chain length epsilon-PL consisting of 5-20 residues at the highest production level of 4.5 g l(-1). This epsilon-PL had different spectra in terms of antimicrobial activity from the epsilon-PL that is now used as a food preservative. The high productivity was based on multiple metabolic pathways for l-lysine synthesis, and a great flux from l-lysine to epsilon-PL. The usefulness of this new epsilon-PL and its producing strain was discussed.