Since the studies of Jacobstahl in 1910, many efforts has been done to show that the complement fixation test for syphilis is more sensitive with cold fixation than with Wassermann's test at 37°C. Undoubtedly, the temperature and the duration of incubation is the important factors influencing the sensitiveness and specificity of the complement fixation reaction. The author studied the above mentioned factors in Ogata's test with cardiolipin aneigen and the resucts were as followed, 1. The complement and hemolysin should be kept and used below 10°C to obtain maximum titer. 2. The results of the heat incubation (I hour at 37°C) showed mostly the same as in cold incubation qualitatively. 3. Cold fixation at 5°C is reliable and with the syphilitic sera showed more sensitive than one hour fixation at 37°C dicidedly.