It has long been known that ovarian tumors in the human are an important cause of sterility and related problems of the reproductive tract. Very little work has been done on this condition in domestic animals. In recent years some veterinarians and some animal husbandmen have considered ovarian tumors, especially the cystic type, as being a cause sterility and slow breeding in cows. It is also known that cystic ovaries may be a cause of nymphomania in the mare and on their removal, recovery is effected.