During the last ten or fifteen years there has been considerable interest aroused by the publications from all over the world (see map) of fevers that resemble Typhus Exanthemus clinically, but which appear to differ in certain respects in their etiology. The fevers that have been described by the various authors are endemic in their respective countries, cases occurring sporadically each year. There does not appear to be any person to person infection in these fevers and this has led to their being differentiated from Typhus Exanthemus which is known to occur in epidemics and has been called an in- fectious disease. It is known that Yyphus Exanthemus can be prevented by the exclusion of lice or its excreta from contact with the individual and so the disease is not strictly speaking infectious, but contagious, infection being passed by means of the louse. In the majority of the fevers that have been described, the carrying agent is thought to be some insect other than the louse. The insects that are suspected are ones that do not habitually live on man but only bite them occasionally, hence the unlikelihood of person to person infectivity in these fevers. The fevers have been given numerous different names, each country and author giving its or his own name for their own special fever, and so there has arisen a great deal of confusion with regard to these fevers. It is the purpose of this thesis firstly, to describe in detail the disease as it is found in Kenya and the results of investigations into its etiology that have been carried out recently, secondly, to give a brief description of the other fevers that occur elsewhere in the world and, thirdly, to endeavour to correlate the various fevers and bring them together into one group and to show that all these fevers are varieties of Typhus Exanthemus.