Intraspecies interrelations between representatives of 7 serotypes of Bacillus thuringiensis, as well as antagonistic interrelations between B. thuringiensis and 130 strains of 16 species of Bacillus bacteria were studied. Antagonistic activity was determined for 18 strains, representatives of genus Bacillus, with respect to B. thuringiensis var. tuviensis. Antagonism was the most pronounced between the strains of the alesti serotype and representatives of other serotypes as well as between the strains V. thuringiensis var. tuviensis and most of other bacillus species. Strain B. thuringiensis var. tuviensis is slightly sensitive to the action of toxic metabolites from strains of this and other species of genus Bacillus.