During summer Mediterranean spotted fever (MSF) is prevalent in the subcostal part of Croatia (North Dalmatia) as well as in other areas of the Mediterranean coast. We compared the specificity and sensitivity of complement fixation (CF), latex agglutination (Latex-R. conorii), microimmunofluorescence (micro-IF) and enzyme-linked immuno assay (ELISA) for detection and measuring antibodies against Rickettsia conorii in 78 sera from 46 patients with/or suspected Mediterranean spotted fever. The seroreactivity with SFG antigens containing the Rickettsia conorii-antigen(s) as a common determinant, was positive in all four serological tests suggesting that Rickettsia conorii was the probable causative agent of infection in our patients.