As many of the problems connected with the infectious diseases of man have been solved, a number of investigators have turned their attention to the course of infection in the individual cell. This contrasts with the interest of earlier workers who were primarily concerned with the course of disease in individual patients or in human populations. The trend toward the study of smaller and simpler universes has been hastened, no doubt, by the recognition of our inability to explain the cause of failures in studies involving such complexities as man. Similar trends toward microcosms are evident in many fields of biology and medicine, as well as in the physical sciences. Today I wish to discuss the use of the infected cell as a model for the study of problems associated with the chemotherapy of the carrier state in man. One of the phenomena about which too little is known is the carrier state and the role of intracellular infection in maintaining this state.