ARNOLD, HOLTZ AND MARX stated in 1936 that dogs treated with large doses of estrogens, estradiol benzoate, in daily doses of 5 mg. of the crystalline substance showed a severe anemia and died from the effects (1). This observation has been confirmed by other investigators (2, 3, 4). Simultaneous administration of androgens (androsterone) andestrogens did not prevent the latter from exerting its toxic action on the animals (3). It has not yet been determined why dogs should be more sensitive to estrogens than other animals including man. Since the metabolism or elimination mechanism in the dog may differfrom that of other animals, it appeared pertinent to analyze the elimination of administered estrogens in the urine and their distribution in various organs. The hormones used were dissolved in olive oil, 1 cc. containing 5 mg. of the crystalline substance. Injections were given subcutaneously.