Abstract
The antibodies active in the Rose Bengal plate test (RBPT) for bovine brucellosis have been studied. The results of fractionation experiments showed that RBPT activity was associated with fractions containing immunoglobulin of the IgG(1) class; other immunoglobulin classes were inactive in this respect although active in other tests. These results were confirmed by inhibition tests with specific antisera and by elution of the antibody from agglutinated RBPT antigen.The major proportion of the serum complement-fixing activity was also present in the IgG(1) fraction and it is suggested that the RBPT and CF reactions are probably mediated by the same antibodies.