BACKGROUND Determine the antibodies prevalence against Coxiella burnetii and Rickettsia conorii in Soria (Spain). METHODS By an indirect immunofluorescence test we examined sera samples for antibodies (IgG, IgM and IgA) against C. burnetii (phase II, formolized antigen) and R. conorii (moroccan strain). The test has been applied to 298 sera (150 men and 148 women) from Soria (Spain). The age of the study population ranged between 2 and 91 years. The results were considered positive when the titres were greater than or equal to 1/80 for C. burnetii and 1/40 for R. conorii. RESULTS Antibodies against C. burnetii were present in 20.8% of the examined sera, 8.8% for women (13/148) and 32.7% for men (49/150). We demonstrated titers of antibodies upper to 1/40 in all age groups, and a greater number of positive results in the persons older than 40 years old (p = 0.0001). In all areas we detected positive results and in many of these areas, the positivity was high (38%). We demonstrated positive results against R. conorii in 5% of the people (4.7% for women and 5.3% for men). More than 90% of the positive cases was present in the eastern part of Soria, and in an small area, the positivity was 20%. CONCLUSIONS These results confirm a high prevalence of antibodies against C. burnetii in the Soria people, and the existence of R. conorii infection in this area of Spain with a particular distribution. We believe that it is very important to establish an epidemiological surveillance for the detection of clinic cases.