Follicular formations, with a structural resemblance to thyroid follicles, and glandular duct-like medullary formations are found relatively often in the adrenal medulla of various ruminants. They occur in the peripheral medullary zone and consequently are comprised of a similar type of cell (A-cells according to Klein and Kracht). Illustrations are given of adrenal follicles in the ox, giraffe, and various deer. The appearance of the follicles coincides in part with pronounced morphokinesia in the entire medullary area, resulting on the one hand in extreme nuclear swelling with increase in volume of the nucleoli, and on the other hand, a sometimes extensive degeneration of the medullary epithelium. The follicular epithelium often shows phenomena of active secretion in the form of vacuoles and production of homogeneous ball-like formations measuring 1–10.5μ. In addition desquamation of the medullary cells and their disintegration can be observed in the follicular lumen. These appearances suggest that the formation of follicles may be considered a morphological manifestation of an acute or extreme functional stress of the adrenal medulla.