Complement binding antibodies against Coxiella burnetii were measured in 699 seric samples in order to ascertain the possible relationship between seric prevalence and the following factors: age, sex, living in rural or urban areas and socio-economical level. All patients were healthy: 180 were from a rural area 86 from Guijo (Cáceres); 36 from Chiloeches (Guadalajara) and 58 from Bustarviejo (Madrid); 519 were from an urban area (City of Madrid). The samples from Madrid city were classified by socio-economical level: 386 from medium-low level (MLL) and 133 from medium-high socio-economical (MHL) level. The global seroprevalence was 32.3%, being 46.1% from rural areas; --59.3 from Guijo, 33.3% from Chiloeches and 34.5% from Bustarviejo. In urban areas the seroprevalence was 27.5% this being 30.8% MLL and 18% MHL. We found a statistically significant relationship between both socio-economical levels and the area of living.