A hemorrhagic syndrome that was soon to become one of the major poultry disease problems in many parts of the United States and Canada was first seen in the Delmarva area in 1951. In Ontario the syndrome was first diagnosed as such in 1954 at the Ontario Veterinary College. Twenty-three cases were encountered in 1954-55,one hundred and sixty-six in 1955-56, and four hundred and sixty-three in1956-57. Most of the birds affected were raised as broilers,although the condition was also found in replacement pullets and turkey poults. In general the symptoms were similar to those of intestinal coccidiosis. The birds appeared listless and droopy with ruffled feathers,pale combs,and wattles; liquid droppings were often noted. On post mortem examination the lesions were small, discrete hemorrhages found mainly in the breast and thigh muscles (Figs. 1 and 2). Hemorrhages were also found in the intestinal wall (Fig. 3) and less frequently in other viscera. Aplastic bone marrow was rarely seen, and in cases uncomplicated with other diseases, no histopathological lesions other than the hemorrhages were found. On the basis of several reports (16, 17, 25, 28) the use of water soluble vitamin K was generally recommended as a treatment. In certain cases good results were reported, but in many others the use of the vitamin did not seam to affect the condition in any way. A number of authors (2, ID, 31* 37) reported that vitamin K had no effect on the hemorrhagic condition. In view of these contradictory findings it was considered necessary to carry out controlled experiments in order to assess the value of vitamin K as a therapeutic measure in the hemorrhagic condition as it is found in Ontario. Because the therapeutic value of vitamin K had to be determined in field cases, specifically, the experimental birds were obtained from farms where a natural outbreak of the hemorrhagic condition was present.