The application of new biotechnology to the study of the biochemistry of rickettsiae was a prominent feature of the presentations at the 3rd International Symposium on Rickettsiae and Rickettsial Diseases, held in Smolenice near Bratislava in September 1984. This review is an attempt to summarize recent advances leading up to these presentations as well as the studies that have been reported in the two years since the meeting. Since rickettsiae are intracellular parasites, most reviews deal with the interaction of rickettsiae with host cells. It is useful, however, to focus also--as we have done--on the properties of rickettsiae that can be demonstrated in the absence of their hosts, although, undoubtedly, many of these properties reflect adaptation to an intracellular microenvironment.