A study was carried out on the species composition, as well as on the biochemical characteristics of 190 strains of aerobic spore-forming microorganisms of the type Bacillus, isolated from fresh and pasteurized milk. The differentiation of bacilli was made following Petrova's diagram [4]. It was established that the bacillary strains studied referred to I morphological group--Bac. licheniformis 55.9%, Bac. subtilis 24.8%, Bac. puminis 14.7% and bac. cereus 4.6%. The results of the experiments that were carried out with regard to the most characteristic morphological, biochemical and cultural properties of bacilli of group I, coincided with the data in Petrova's diagram. The bacillary strains that were isolated showed high biochemical activity with regard to proteins and carbohydrates, which is of paramount importance for the hygiene and quality of fresh and pasteurized milk.