The virulence of 250 pathogenic Escherichia strains secreted from humans and from various environmental objects has been studied on nutrient media with stains, ram erythrocytes and in hemagglutination reactions. The highest percentage of strain virulence is revealed when using crystal violet and in the blood agar (44.0 and 27.2%, respectively), evidently, due to nonspecific reactions. The medium with congo red showed a positive result in 20.3 + 3.1%, and the d-mannose-resistant hemagglutination reaction--in 16.5 + 2.3% cases. In practice it is recommended to use several methods which enable estimating correctly the risk to infect humans and to conduct timely preventive measures.