Current methods of chemotherapy and chemoprophylaxis of pyogenic bacterial infections leave much to be desired. Alternatives that are potentially applicable to man may be found among the antagonistic interactions of microorganisms that serve to maintain an ecologic stability within the microcosm. Investigations in this area must be designed to (1) detect naturally occurring antagonistic interactions between man's indigenous microflora and human pathogens and (2) study the potential for exploitation of these interactions in prevention of pyogenic infections. Specific goals, both immediate and long term, of the proposed research include (1) detection of antagonism of group A streptococci, staphylococci and meningococci by strains of the normal throat flora in vitro, (2) demonstration of the extent to which the presence of these antagonistic strains contribute to host resistance to infections, (3) determination of the mechanisms of those antagonisms that appear to be operative in man, and (4) evaluation of the qualitative and quantitative effects of (a) antimicrobial therapy, (b) antiseptics and (c) epidemiologic parameters, such as age, socioeconomic status and family grouping, upon the naturally occurring antagonisms resultant from the normal flora. BIBLIOGRAPHICAL REFERENCES: Sanders, C. C., Sanders, W. E. Jr., and Harrowe, D. J. Bacterial Interference III: Effects of Oral Antibiotics on the Normal Throat Flora and Its Ability to Interfere with Group A Streptococci. Infection and Immunity. 13:808-812, 1976. Sanders, W. E. Jr. Drugs Five Years Later: Rifampin. Annals Internal Medicine, 85:82-86, 1976.