Boza is a low-pH and low-alcohol cereal-based beverage produced in the Balkan Peninsula. From a total population of 9 x 10(6) colony-forming units ml(-1), four isolates (JW3BZ, JW6BZ, JW11BZ, and JW15BZ) produced bacteriocins active against a broad spectrum of Gram-positive bacteria. Bacteriocin JW15BZ inhibited the growth of Klebsiella pneumoniae. The producer strains were identified as Lactobacillus plantarum (strains JW3BZ and JW6BZ) and L. fermentum (strains JW11BZ and JW15BZ). The spectrum of antimicrobial activity, characteristics, and mode of action of these bacteriocins were compared with bacteriocins previously described for lactic-acid bacteria isolated from boza.