I WISH to describe two methods I have used of transplanting whole mammary glands in goats. The work was undertaken so that mammary function could be studied in conscious undisturbed animals, by experimenting on one gland and comparing it with the control gland on the same animal. Anaesthesia reduces the rate of milk secretion, and it is not easy, for example, to make repeated flow measurements or arterial infusions in conscious goats because the main artery is difficult to exteriorize effectively. By transplanting one gland on to another site on the animal, the main artery and vein are made readily accessible. It is well known that mammary growth and milk secretion can take place after the nerves to the tissue have been removed, and it is generally believed that these processes are almost entirely controlled by hormones. Although Ribbert showed in 1898 1 that small pieces of mammary tissue survive autotransplantation and show histological signs of normal growth and function, there have been no reports of the transplantation of whole glands nor of the quantitative measurements of growth and lactation of denervated tissue that are possible with the present methods.