Comparing 50 hypophysectomized [female] albino rats with 50 controls 2 wks. after operation: mean hypophysis-wt. of operated rats was 25% greater than that of controls (statistically significant); mean value of relative % of hypophysis wt. to body wt. of operated group was 27% greater than control group (significant). Microscopic examination of hypophyses of splenectomized animals indicates increased vascularity, increased reticulo-endothelial cells, hyperplasia of basophile cells.