Groups of 10 to 14 castrated female BALB / c mice received viable uni- or bilateral intraocular isografts of one-eighth or of one-thirty-second of an ovary. Ten other animals remained intact. At biopsy five months later, the mammary glands of all animals showed little or no stimulation. Most animals with one or two one-eighth or two one-thirty-second, grafts had shown normal vaginal and ovarian cycles prior to this time, but some had been in continuous metestrus and had acyclic grafts with vesicular follicles. Most animals with one one-thirty-second grafts were similarly in metestrus, but some were in diestrus with grafts lacking follicular structures. At autopsy eight months after grafting, almost all mice with one or two one-eighth grafts had alveolar proliferaiton with secretion in the mammary glands. All were in continuous metestrus with acyclic grafts, and most had uterine cystic hyperplasia and peri-medullary adrenal degeneration. At the same time, slightly more and slightly less than a half of the mice with one or two one-thirty-second grafts, respectively, showed these same abnormalities. Intact mice were devoid of them. The development of this mammary-uterine-adrenal syndrome appeared to be directly related to grafted ovarian tissue per se and to the size of the grafts. It may depend upon a pituitary-ovarian imbalance with a failure of LH release.