Evidence has been obtained1that sulfanilamide may modify the course of experimental tuberculosis in guinea pigs. Similar results were reported for sulfapyridine2and for azosulfamide.3These results now have been confirmed by a sufficient number of laboratories to require their acceptance. The effect of these drugs appeared to be one of retardation of the rate of development of the disease in treated animals when they were compared with untreated controls. In addition a definite alteration in the histologic features of the lesions was described.4 Our first experiment with sodium p,p′-diaminodiphenylsulfone-N,N′-didextrose sulfonate5established the fact that this drug could inhibit, partially or totally, the development of experimental tuberculosis in guinea pigs. In this experiment treatment was started two days before inoculation with human tubercle bacilli. The conditions of this earlier experiment did not simulate natural infection, since the infecting organism had been introduced into animals already