The diarrhea of newborn calves in Wisconsin is characterized by a watery, yellow diarrhea which begins 1 to 2 days after birth. The age at which the calf is exposed, the feeding of colostrum, and the method of exposure are critical factors determining the character of the clinical manifestations of the experimental disease. The fact that the aerosol method of exposure was the means by which the acute type of the disease has been produced suggests that this is largely an air-borne disease. The etiological agent of this disease has been characterized as a virus. Serial transmission of a bacterial free inoculum in calves together with serial passage in the gravid uterus of mice and guinea pigs have been 'accomplished.