Mediterranean spotted fever is a rickettsiosis due to R. conori. The authors have tested 2 serological reactions available in this disease: Weil-Felix (WF) and indirect immunofluorescent antibody test IF. IF, tested on 184 sera is sensitive (100% of positivity 30 days after the onset of the disease) and specific if a four fold in two sera is obtained at a level upper than: 80. The WF tested on 112 sera is not specific and its sensitivity is poor.