Nisin Z and thymol were tested, alone and in combination, for antibacterial activity against Listeria monocytogenes ATCC 7644 and Bacillus subtilis ATCC 33712. The antibacterial effect of nisin Z, produced by Lactococcus lactis KE3 isolated from the traditional Moroccan fermented milk, was greatly potentiated by sub-inhibitory concentrations of thymol in both bacterial strains. Our data showed that the concentration of nisin required for effective control of food-borne pathogenic bacteria could be considerably lowered by the use of thymol in combination. The use of low concentrations of nisin could lead to a less favourable condition for the occurrence of nisin-resistant bacterial sub-populations.