Fluorescence polarization immunoassay (FPA) uses molecular rotational properties to measure antibody binding to antigen directly. The potential use of this method was assessed in comparison to a competitive enzyme immunoassay (CELISA) and conventional serological tests for the diagnosis of brucellosis on a total of 587 human sera. Based on 340 sera from asymptomatic blood donors with no evidence of brucellosis, the specificity of the FPA was 97.9 % using a cut-off value of 72 mP. Sera from Brucella-infected patients (11 Brucella melitensis, 32 Brucella abortus, 32 Brucella suis and one Brucella sp.) yielded a sensitivity estimate of 96.1 %. In tests on 84 sera from suspected brucellosis patients, the FPA detected 80 cases. Of 87 sera from patients with probable infection, 15 were detected by both CELISA and FPA, three by CELISA only and four by FPA only. The discrepancies in both groups involved sera with low, declining titres. The FPA uses a sample of 40 micro l serum, takes about 5 min to complete and has been demonstrated to be accurate for the detection of antibodies to B. abortus, B. melitensis and B. suis and for identifying patients suffering relapses. Because of the ease of the procedure, it could be readily adopted for use in clinical laboratories and blood banks.