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Few reports have appeared on the growth of transplantable tumors in hypophysectomized animals. Ball and Samuels( 1,2) were the first to show that the growth rates of 2 transplantable sarcomas were markedly slower in hypophysectomized rats than in intact controls. They were able to demonstrate that the retardation was due to the absence of pituitary secretions per se ( 3 ,4) . Loefer (5) and Franseen and McTiernan(6) have also noted retardation of transplanted tumor growth in hypophysectomized rats. McEuen and Thornson(7) observed retardation of growth of transplanted Walker tumors in hypophysectomized rats; they concluded, however, that the slower growth was not due entirely to the absence of pituitary secretions, but in part to the dietary restrictions suffered by hypophysectomized animals. When hypophysectomized and intact rats were maintained on the same food intake, these investigators observed no difference in tumor growth between the 2 groups. Recently, Talalay and associates (8) have demonstrated that the growth of intramuscular implants of the Walker tumor was inhibited in hypophysectomized animals to about 46% of that in intact controls when both groups were tube fed and their body weights maintained at approximately the same level.All of the above observations were made in the rat and the author is aware of only one other reported study carried out in mice (9). By grafting spontaneous mammary carcinomas obtained from dilute Brown-Murray-Little strain mice into hypophysectomized and t The author wishes to express her sincere appreciation to Dr. Henry S. Kaplan and to Miss Mary B. Brown and Miss Barbara H i r d for their kind assistance.intact groups of animals, Korteweg and Thomas(9) found no difference in tumor growth between the 2 groups. These investigators concluded that since the grafted tumors grew perfectly well in hypophysectomized mice, the influence of the pituitary is not a qualitative one, and if any influence exists, it can be only quantitative in nature. The present study was undertaken to determine whether radiation-induced 1 ymp hoid tumors of C57BL mice are capable of growing in hypophysectomized mice. Materials and methods.One hypophysectomized and one intact group of mice were used in this experiment. Hypophysectomies were performed on 8 female and 6 male immature C57BL mice, 30 to 40 days of age and weighing 14 to 20 g, by the parapharyngeal method of Thomas( 10) modified by the use of an Elliott corneal trephine to cut a window in the base of the skull. The animals were maintained in a warm room at 80 t 2 O F on a diet of bread soaked in Brewer's yeast-enriched milk,$ lettuce, carrots, and Purina laboratory chow, and were given a 5% glucose and 0.9% sodium chloride solution as drinking fluid.. Eight male and 8 female control animals were sham-operated and were also maintained, on the above regimen except that tap water was given as drinking fluid. The experiment was started one month after the operative procedure, thus allowing sufficient time for the: animals to recover. At this ...