A homogeneous fluorescence polarization assay (FPIA) for detection of bovine antibody toBrucella abortuswas validated in Argentina. Sera were defined based on their reactivity in the buffered antigen plate agglutination test (BPAT) and the competitive enzyme immunoassay (CELISA). Sera negative in these tests were collected from farms without evidence of brucellosis (n=733). Sera positive in the two tests were collected from cattle on farms from whichB. abortuswas isolated from at least one animal (n=1039). Sera from cattle vaccinated 26, 89, 240 and 272 days previously withB. abortusstrain 19 were collected and tested. A cut-off value of 87 mP was determined for the FPIA, resulting in relative sensitivity and specificity values of 98.1 and 99.6%. the specificity forB. abortusstrain 19 vaccinated cattle was 64.9% (26 days post vaccination, DPV), 92.1% (89 DPV), 98.6% (242 DPV) and 97.1% (272 DPV). These values were compared to those obtained with the BPAT, the CELISA, the indirect ELISA, the complement fixation test and the 2-mercaptoethanol agglutination test. Sera from 18 cattle which were vaccinated and revaccinated withB. abortusstrain 19 were also tested by the same assays and the FPIA was found to be 100% specific. the use of the FPIA as a diagnostic test for brucellosis is discussed.