The continuous production of nisin, an antibiotic polypeptide, by Lactococcus lactis in a bioreactor system coupled to a microfiltration module is described. Nisin productivity with respect to both cultivation time (ND) and the quantity of glucose consumed (ND/S-f) in continuous production was enhanced by maintaining a low concentration of lactic acid in the broth. A maximum ND of 7.80 x 10(4) U.l(-1).h(-1) and ND/S-f of 5.20 x 10(3) U.g(-1).h(-1) were obtained when the glucose concentration in the feed medium was 15 g/l. These values represent about 4.1- and 4.5-fold increases, respectively, over those obtained in batch culture.