This paper deals with studies on epsilon-poly-L-lysine (epsilon-PL) production in an airlift bioreactor (ABR) using Streptomyces albulus S410 (S410) to minimize the production cost including the downstream processing of epsilon-PL. In a 5-l ABR, 30 g/l of epsilon-PL was produced with a power consumption of 0.3 kW/m(3), the production level being similar to that in a 5-l jar fermentor with a power consumption of 8.0 kW/m(3). Furthermore, the leakage of intracellular nucleic acid (INA)-related substances into the culture broth in the ABR was less than that in the jar fermentor. Due to the high-level power consumption (8.0 kW/m(3)) in the jar fermentor, the morphology of the cells changed from the pellet to filament form due to the extensive shear stress arising from continuous agitation, thereby increasing the leakage of the INA-related substances into the culture broth. This suggested that ABR would have an advantage in the low-cost production of epsilon-PL over stirred tank type reactors (STR).