The antigen-to-saline drop method was found to be the best method for the preparation of antigen emulsions suitable for the passive hemagglutination reaction by the phosphatide of tubercle bacilli. Ordinary saline or buffered saline at pH 7.0 and 8.0, prepared by adding 1/10 volume of phosphate buffer at respective pH values, was found suitable for obtaining the reaction. The sensitization of erythrocytes and the reaction of the mixtures of antigen and sensitized erythrocytes took place satisfactorily at 37[degree]C for 30 minutes. Of the complement-fixation, precipitation, and hemagglutination tests, the last-named gave the highest antibody titers. Upon addition of complement, the phosphatide hemagglutination reaction was converted to the hemolytic reaction, giving still higher antibody titers.