1. An infection ("carrier state") could be established predictably in every animal exposed to the aerosol inoculum.

2. Infection was limited to the upper respiratory tract and occurred without apparent systemic dissemination.

3. Cross-infection between infected and non-infected animals did not occur.

4. The initially established infection persisted in detectable form for 6 days or less in the majority of exposed animals.

5. Tetracycline administration prior to and following aerosol infection with tetracycline-resistant strains significantly prolonged the duration of the carrier state.

6. When tetracycline-resistant strains were employed, the infection could be recalled predictably by means of tetracycline administration.

7. Infection initiated with a tetracycline-susceptible strain could not be recalled by tetracycline administration.

8. The mechanism(s) of action of tetracycline in recalling the attenuated infection is (are) unknown. It (they) may not be wholly attributable to ecological changes alone, at least as these are usually considered. The indigenous microflora diminished and changed as a result of tetracycline administration, and no growth-enhancing effect of the antimicrobial of the infection strains was detectable in vitro.

9. The experimental model described lends itself well to the study of attenuated staphylococcal infection in guinea pigs, and to more general studies of staphylococcal epidemiology and pathogenesis.