A considerable bacterial and fungal populations are lived on the aerial surfaces of tomato plants even at the age of 8 weeksTwo epiphytic bacterial strains and two epiphytic yeast ones proved to be highly antagonistic against the tomato pathogens (Pseudomonas syn'ngae pv. tomato and Xanthomonas campestris pv. Vesicatorfa)in vitro studies. One of the most antagonistic bacterial strains belongs to the genus Bacillu sand the other one belongs to the genus Pseudomonas.The two most antagonistic yeast strains taxonomically belong to the genera Aureobasidium and Cryptococcus. 0n the base of their in vitro antagonism, the most effective antagonistic bacterium, i.e. Pseudomonas sp. and the most effective yeast strain, i.e. Crxotococcus sp. were tested in pot experiments. Both the tested bacterium and the yeast strain showed a significant antagonistic effect against Pseudomonas syringae pv. tomato and Xanthomonas campestn's pv. vesr‘caton‘a. The preventive effect of the two selected microbes on the bacterial speck and bacterial spot diseases was exhibited in a preliminary pot experiment too.