Improved hypophysectomy technique and the efficacy of bGH in hypophysectomized female rats were studied as a basis for the function of endocrine gland and hormones. 1. With improved sublaryngeal a, pp.oach by hypophysectomy, 34 rats out of 40 were successfully hypophysectomized(more than 80% of success). The surgical time for hypophysectomy per rat was taken about 3.0$pm$1.0 min. 2. For the effect of hypophysectomy and bGH on body weight gain among the 5 gruops of A, B, C, D, and E, the weight gains for A, B, C, D, and E, were 93g, 9.2g, 10.7g, 25.1g and 36.2g, respectively, which implied that hypophysectomy had a major effect on body weight. And also, the effect of bGH was paralleled with the level of bGH. There were significant difference between control and hypophysectomized groups, and between the bGH treated and bGH non-treated groups after hypophysectomy(p<0.01). 3. For the effect of hypophysectomy and bGH on the length of femur, tibia, humerus, and anterbrachi, longest was for A, shortest for B, and longer in order of C, D, and E. The A group was significantly longer than B, C, D, and E groups. The B group was shorter than C, D, and E groups(p<0.01). 4. For the effect of hypophysectomy and bGH on the weight of femur, tibia, humerus, and antebrachi, heaviest was for A, lightest for B, and heavier in order of C, D, and E. The A group was significantly heavier than B, C, D, and E groups. The B group was lighter than C, D, and E groups(p<0.01). 5. In changes of body length, and weights of liver and heart, A group was most drastically increased. Among the hypophysectomized groups, the change was increased in order of B, C, D, and E. Especially, the change of A group was significantly greater than B, C, D and E gruops. However, no significant differences were found among B, C, D, and E groups. 6. The hypophysectomy in rat had a significant effect on body growth. The effect of hormone was remarkably different depending upon the level of hormone. It was found that 300$mu extrm{g}$ of bGH/kg of body wt/day was slightly lower for normal growth.