Brucella ceti causes disease in Odontoceti. The absence of control serum collections and the diversity of cetaceans have hampered the standardization of serological tests for the diagnosis of cetacean brucellosis. Without a "gold" standard for sensitivity and specificity determination, an alternative approach was followed. We designed an indirect enzyme-linked immunosorbent assay (iELISA) that recognizes immunoglobulins G (IgGs) from 17 odontocete species as a single group. For the standardization, we used Brucella melitensis and Brucella abortus lipopolysaccharides, serum samples from seven resident odontocetes with no history of infectious disease displaying negative rose bengal test (RBT) reactions, and serum samples from seven dolphins infected with B. ceti. We compared the performance of the iELISA with those of the protein G ELISA (gELISA), the competitive ELISA (cELISA), and the immunofluorescence (IF) and dot blot (DB) tests, using 179 odontocete serum samples and RBT as the reference. The diagnostic potential based on sensitivity and specificity of the iELISA was superior to that of gELISA and cELISA. The correlation and agreement between the iELISA and the gELISA were relatively good (R i/g 2 ؍ 0.65 and i/g ؍ 0.66, respectively), while the correlation and agreement of these two ELISAs with cELISA were low (R i/c 2 ؍ 0.46, R g/c 2 ؍ 0.37 and i/c ؍ 0.62, g/c ؍ 0.42). In spite of using the same anti-odontocete IgG antibody, the iELISA was more specific than were the IF and DB tests. An association between high antibody titers and the presence of neurological symptoms in dolphins was observed. The prediction is that iELISA based on broadly cross-reacting anti-dolphin IgG antibody would be a reliable test for the diagnosis of brucellosis in odontocetes, including families not covered in this study.Brucellosis is a disease of terrestrial and marine mammals and a relevant zoonosis caused by intracellular bacteria of the genus Brucella (34). In the last 2 decades, several strains of Brucella have been isolated from marine mammals, primarily from dolphins, porpoises, and seals (6, 11, 13-16, 18, 28, 42, 43, 49). For these marine strains, species names were proposed, first as a single cluster called "Brucella maris" (27) and, thereafter, divided into "Brucella cetaceae" and "Brucella pinnipediae" (7). Recently, the proposal of incorporating these marine strains as two new species was accepted; however, their names were corrected to Brucella ceti and Brucella pinnipedialis (15). The former Brucella species is predominant in dolphins and whales, while the latter is mainly isolated from seals and sea lions. These two new marine Brucella species can be further divided into several strains according to molecular biotyping (20), indicating that the species group is heterogeneous. The marine species display phenotypic resemblance with smooth Brucella abortus and Brucella melitensis, possessing the same relevant surface antigens that are commonly used for the serological diagnosis of brucellosis in bovines,...