Fifteen different Rose Bengal antigens showed large differences with respect to pH, cell concentration and agglutination with the international standard anti-Brucella abortus serum, demonstrating the lack of international standardisation. Their sensitivity and specificity, compared with that of the complement fixation test, were evaluated for the diagnosis of B melitensis infection in culture-positive sheep, brucella-free ewes, and sheep and goats belonging to field flocks under different epidemiological conditions. All the Rose Bengal antigens and the complement fixation test had 100 per cent specificity when testing brucella-free sheep or animals belonging to flocks in unvaccinated brucellosis-free areas, but there were large differences in sensitivity between the Rose Bengal antigens with sera from culture-positive sheep or from animals belonging to infected flocks. When using the most sensitive antigen, no difference was observed in Rose Bengal sensitivity between animals infected with either biovar 1 or biovar 3 of B melitensis. The relationship between the sensitivity of the Rose Bengal antigens and cell concentration was unclear, but their sensitivity was related to the standardisation of the antigens with the international standard serum. The complement fixation test was less sensitive than the Rose Bengal test when testing culture-positive sheep. When testing sera from animals belonging to infected flocks with antigens standardised according to European Union rules, no great differences were observed in the sensitivities of the two tests. However, great differences in sensitivity between the Rose Bengal antigens were observed with sera from animals belonging to flocks with low levels of prevalence.(ABSTRACT TRUNCATED AT 250 WORDS)