From the literature on leptospiral infections in the United States, Weil's disease (spirochetal jaundice) and canicola fever.1it would appear that these diseases have been recognized as a problem in preventive as well as curative medicine, as prophesied editorially inThe Journal of the American Medical Associationten years ago.2The research, devoted to this subject since Weil made his clinical observations in 18863has resulted in much valuable information. The spirochetè Leptospira icterohaemorrhagiae was established as the causative organism of Weil's disease in 19154Laboratory methods for its diagnosis were introduced in 1922.5The clinical manifestations, pathology, animal reservoirs, epidemiology and geographic distribution have been extensively discussed in the literature.6A comparable, but less complete, elaboration of detail is also available for canicola fever.7 Despite this wealth of data, however, leptospiral infections still challenge the public health officer, the clinician, the bacteriologist, the laboratorian,