The present study was undertaken to determine the efficacy of bismarsen (bismuth arsphenamine sulphonate) in Wassermann-fast syphilis. This aspect of the disease is of common incidence, and its management from a serologic standpoint has, up to now, proved far from being entirely successful. This is evidenced by the various drugs which have been advocated to combat it. The employment of bismuth compounds has been accompanied by a fair measure of success; yet a reversal in the serology in from 25 to 33 per cent of the patients so treated is about the best that may be hoped for or accomplished.1 Treatment with sulpharsphenamine2 has been recommended, but has evidently proved to be without value.3 More recently, Stokes, Miller and Beerman,4 in recording the results which they obtained with bismarsen in the various forms of syphilis, reported their degree of success in the Wassermann-fast