During 1924 and 1925 in the United States, exclusive of Texas, Arizona and New Mexico, ten cases of undulant fever were recognized in six widely separated states. During 1928 and the first five months of 1929, more than a thousand cases were diagnosed and these had their origin in forty-two states. This increase in the recognition of the disease has been brought about by a growing awareness of its presence, and the further spread of knowledge will undoubtedly result in the recognition of more and more cases. It is my purpose, therefore, to present some of the salient points in the newer knowledge of this disease. That the data are incomplete may be apparent, but for this an apology is not necessary, since in the study of undulant fever the obtaining of complete and accurate information is dependent on the active cooperation of informed physicians. Conclusions at this time would