In a recent communication1 I presented a comparative study of the value of the Wassermann and Noguchi methods for the serum diagnosis of syphilis. The latter was shown to be more sensitive in syphilis, but sera from seventeen non-syphilitic patients were positive with this method and negative with the Wassermann. Attention was called to the fact that eight of the non-specific reactions became negative when inactive serum was substituted for active. The question then arose : Does inactivating destroy the value of the method with syphilitic sera? The present communication is a report of the work done to determine this point. The simplicity of the Noguchi technic2 makes it the most desirable method for general use, if it can be so modified that it is as reliable as the original Wassermann procedure. The principle of the two methods is the same; that is, the suspected serum, the