Twenty-four cases of syphilitic patients were treated with Neo-Spirarsen. Fifteen cases of them were minutely recorded, i.e. three cases of hard chancre, seven cases of syphilis secundaria, five cases of syphilis tertiana. From the results obtained here, the therapeutic efficiency and the toxic reaction may be summarized as follows: The occurrence of toxic reaction was found to be decidedly less. Among 142 injections, high fever was occurred in one to every two patients after the injection, but wereapontaneously subsided after several hours. Concerning the toxicity, there is nothing else to be stated. All chancres were disappeared after one or two in jections of Neo-Spirarsen No.2 or No.3. In almost of all the early syphilis, the complete reversal of the blood serologic test was obtained after the injection of about 4 grams of this drug. In the case of late syphilis, at least, there were remarkable changes in the serologic test from strongly positive to weakly positive after several grams of Neo-Spirarsen-injection. In view of this, it is suggested that Neo-Spirarsen will be prove valuable in all stadiums of syphilis.