A micro-agglutination test method for detecting antibodies to Brucella canis was developed. Heat-killed Brucella canis antigens were diluted to an optical density of 0.8 at 420 nm using a spectrophotometer. A volume of 0.025 ml of the antigen was incubated with the same volume of serially diluted sera for 18 to 24 hr at 37 C. Titers of selected dog sera obtained by the present micro-test method were well correlated with those obtained by the classical tube test with satisfactory reproducibility. The micro-test method is more advantageous for screening the antibodies of dog sera because the test can be performed with: (1) smaller volume of the test sera and the antigen (2) shorter period for incubation, and (3) lesser labor.