Ixodid ticks are an important link in the ecology of rickettsiae. Some tick species became specific vectors as well as reservoirs of certain species of rickettsiae ensuring their long lasting maintenance via interstadial and transovarial transmission often over generations in nature. To now many significant questions on relationship between ticks and rickettsiae became clear, however, most of them still remain to be elucidated. The open question, for instance, involves the data on the differences in sensitivity of various tick species to a certain species of rickettsiae what has its significance concerning the transmission of an agent to a host. Intracoelomal injection of a tick with rickettsiae does not solve its role as a vector in nature, because the main natural barrier of tick organism against pathogens, i.e. alimentary tract with its specific biochemical properties, has been avoided. To specify a tick as a vector of rickettsiae, data on their maintenance in various developmental stages of the arthropod as well as transmission to a host through feeding the blood are desirable. More attention should be focused to investigation on antibacterial (antirickettsial) effect of lysosyme, interferon and cellular elements in arthropods. Certainly mixed infections in ticks and namely their interactions, as well as the significance of rickettsia-like organisms in these arthropods, require also further investigations. Sufficient conclusive evidence concerning the effect of vector's organism on the biological properties of rickettsiae or in reverse, are almost unavailable. Investigations on above problems require the involvement of the modernest methods of immunology, immunochemistry, biochemistry and morphology.