The inhibition of some undesirable microorganisms namely Escherichia coli, Staphylococcus aureus, Salmonella typhimurium, Listeria monocytogenes and Bacillus cereus in fermented milk (Zabady) by mixed cultures of yoghurt (Streptococcus salivarius subsp. thermophilus and Lactobacillus delbreuckii subsp. bulgaricus) was studied. Results of this study revealed that acidity of Zabady treatments increased, while pH values decreased throughout storage period.  The rates of increasing acidity and decreasing pH values were higher in treatments stored at room temperature than those stored at 5-7°C.  Counts of target organisms declined sharply in the presence of lactic starter.  The rate of disappearance at room temperature was higher than that at 5-7°C.  The inhibition zone varied with the different target organisms.  Supernatant obtained from the harvest of lactic culture incubated at room temperature had higher inhibitory effect than that at 5-7°C.  Non boiled fluid had greatest effect than boiled extracts.