Pain just tolerable was caused intermittently by electric stimulation on rat's tail or by distented baloon in stomach for 30 min. The changes of intermediate lobe are summarized as follows: (1) The cell body, nucleus or nucleolus was hypertrophied. The number of rough endoplasmic reticulum, particularly of its vesicular cisternae was increased. Golgi complex enlarged. The ribosome multiplied. All of these change indicated that the activity of cells was increased and the rate of synthesis enhanced. (2) Both the secretory granules shifted to the periphery of cell body and some of them showed pale density. These changes were interpreted as increase of seretory activity. (3) The mitochondria became enlarged and the crsitae in them were changed into tubular form. This suggested an acceleration of cell metabolism, which might provide a large amount of energy. (4) There was no degenerative change. (5) The cytological changes caused by visceral pain were simillar with, but more striking than, those caused by somatic pain. (6) The secretions were increased, among which ?-endorphin and ACTH etc were known to be closely related to analgesia.