Receptor substances for temperate phages, which were isolated from lysogenic Sh. dysenteriae strains, were tested. These substances were obtained from Sh. boydii 15-7489, which served as an indicator and propagating strain, and from Sh. dysenteriae 2 and Sh. dysenteriae7, which were indicator strains. On the basis of agglutination and precipitation testa, Sh. bodii 15-7489 and Sh. dysenteriae 2 were shown to be serologically related while no relationship was found between Sh. boydii 15-7489 and Sh. dysenteriae7. According to experimental data, it was suggested that phage receptor sites are localized in the protein component of the somatic antigen. This component, occurring in all three examined strains, possessed common antigen properties, as was shown by use of receptor neutralization test.