Brucellosis is a systemic infectious disease caused by Gram-negative bacilli, the genus Brucella, and clinical features are diverse. Therefore, several infectious and non-infectious diseases are considered in its differential diagnosis. In this study, we aimed to determine the positivity rate of Brucella agglutination tests in the culture-positive brucellosis and in diseases mimicking brucellosis clinically.Thirty patients with culture-positive brucellosis, and 280 patients with the diseases mimicking brucellosis clinically (20 with miliary tuberculosis, 33 with malaria, 20 with typhoid fever, 20 with adult-onset Still's disease, 47 with systemic lupus erythematosus, 50 with rheumatoid arthritis, 27 with sarcoidosis, and 63 with active lymphoma) were included in the study. Brucella agglutination tests (Rose-Bengal and Wright) were studied in serum samples of these 310 patients. Both Rose-Bengal and Wright tests (the latter in a titer of 1/160 or higher) were positive in all patients with brucellosis. For the other diseases, the test was slightly positive (1/40) in one patient with malaria and another with non-Hodgkin's lymphoma, and weakly positive (1/20) in a patient with typhoid fever. It remained negative in the remaining. In conclusion, agglutination tests currently used in the diagnosis of brucellosis are very sensitive and specific. Brucellosis can be effectively excluded from the diseases having similar clinical features by the use of agglutination tests.