A microimmunofluorescence technique for the diagnosis of Q fever is described. Although this method is useful for serological diagnosis of Q fever, some technical difficulties are associated with it. First, the test antigens must be produced by a cell culture method in a level-3 biohazard facility and, second, the antigen Coxiella burnetii, which is the causative agent of Q, is characterized by the presence of two phases. To obtain phase I antigen, mice must be inoculated with C. burnetii. The materials obtained from the spleens of the infected mice are then used for cell inoculation. After purification, the antigens of both phases are deposited and fixed on multiple-well microscope slides. The serially diluted sera to be tested are incubated on these slides, then rinsed and overlaid with anti-IgG, -IgM and/or IgA secondary antibodies. Finally, the slides are examined under a fluorescence microscope for presence of C. burnetii.