The presence of antibodies was determined in the serum and cerebrospinal fluid in six patients with neurobrucellosis using the Rose Bengal test, the microdilution agglutination test, and the Coombs' test. Four of the patients were followed up for more than three months. The Rose Bengal test and the microagglutination test were positive in cerebrospinal fluid in five of the six cases at some stage. The Coombs' test was positive in cerebrospinal fluid in every patient and in one was the only positive serological test. Cerebrospinal fluid positivity is not excluded by low titres or negative results of antibodies in the serum for any of the three methods. A Coombs' test or some equivalent must always be made on the cerebrospinal fluid to diagnose neurobrucellosis.