Influences of temperature, the concentration of saline solution as well as various sugars have been studied at the time when the reaction is taking place in the mixture test of precipitin reaction. 1) Temperature of 37°C has been found to be most suitable in enabling the reaction to take place to the highest degree; and the influence of temperature is most prominent on the reaction of ovoalbumin system. 2) As for the influence of the concentration of saline solution, it is most marked when antigen is diluted with distilled water; but the reaction falls behind as the concentration of saline solution more increases. Moreover, Uhlenhuth's method exerts more influence on the reaction than Ogata's antigen-antibody dilution method. 3) The precipitin reaction performed by diluting antigen antibody with the use of various sugars decline than the reaction performed by diluting antigen and antibody by physiological saline solution. 4) The reaction taking place when antigen alone is diluted by saline is stronger than the reactions observed in the case where antigen and antibody are diluted by the same kind of sugar solution. 5) The inhibitory action of sugars on the reaction has been found strong in the order of galactose>saccharose>glucose>sorbit>mannit.