A strain of the murine typhus virus has been isolated from wild rats captured in an Egyptian village. The virus has been passaged twelve times up to date through guineapigs, and has produced consistent febrile and Neill-Mooser scrotal reactions in these animals. Rickettsia have been grown from the tunica vaginalis of infected guinea-pigs in tissue cultures. Rabbits inoculated with the virus have produced serum agglutinins for Bacillus proteus OX19. Inoculation of white rats with the virus failed to produce any detectable effect, although actual infection was proved by inoculating rat brain emulsion into guineapigs.