A micromethod has been developed for the standard agglutination and antihuman globulin tests for serum antibodies to Brucella abortus. The test uses a haematoxylin-stained antigen. The test is simple and quick to perform and, in a comparison at two centres involving 367 sera, the micromethod was found to be more sensitive than the classical test. It is highly suitable both for routine serological screening and for large-scale surveys of occupationally exposed industrial groups.