In this report we attempt to evaluate the prevalence of antibodies against Rickettsia conorii, R. typhi, Coxiella burnettii, and Ehrlichia chaffeensis in central Tunisia. Five hundred sera from blood donors, collected between March and June 1993, were tested for these 4 antibodies using an indirect immunofluorescence antibody assay (IFA). Nine percent of the sera had antibodies against R. conorii (IgG > 1:32) by IFA, and 8% by Western blotting; with IFA, 3.6% had antibodies to R. typhi, 26% to C. burnetii (> 1:50), and none to E. chaffeensis. Infection rates with R. conorii and R. typhi did not differ significantly between the sexes, but fewer young people had antibodies to R. typhi. A significantly higher prevalence of antibodies to C. burnetii was noted for males with no difference between age classes. No significant difference was detected between urban and rural areas. This study confirmed the endemicity of rickettsioses, and revealed a high seroprevalence of Q fever, in central Tunisia.