The study of tryparsamide as an agent for the treatment of trypanosomiasis and syphilis is now approaching a decisive stage, having passed successively through a period of laboratory investigation and a period of preliminary clinical investigation. The results that have been reported on the one hand by Pearce,1by Chesterman2and by Smillie,3and on the other by Lorenz, Loevenhart, Bleckwenn and Hodges,4and by Moore, Robinson and Keidel,5supplemented by numerous personal reports from still other clinicians, leave little doubt that, used with discrimination, tryparsamide will prove valuable in the treatment of human and animal trypanosomiasis and of certain forms of syphilis. Thus far, each step in the progress of these investigations, from the synthesis of the drug to its application to the treatment of diseases, has proceeded as a logical development, based at first on pure experimental evidence and later on clinical experience