In this Fourteenth Annual Lecture in honor of Dr. Charles Franklin Craig I shall review the significant advances which have been made in the last two years in the treatment of the rickettsial diseases and of typhoid fever. The finding that chloramphenicol and aureomycin are highly specific therapeutic agents for the rickettsioses and that chloramphenicol occupies a similar place in the treatment of typhoid fever has provided us, for the first time, with means for the adequate care of patients with these diseases. Today I wish to present certain data illustrating the findings which form the basis for the conclusion that we now have good therapeutic agents for the treatment of these infections. In addition, I wish to discuss certain observations and implications in the field of preventive medicine which should be considered in light of the availability of these specific therapeutic agents.