Changes in antidiuretic substance (i.e., vasopressin) release from the cut pituitary stalk and the intact pituitary gland were observed during electrical stimulation of amygdala medial nucleus. Electrical pulses of 4 or 36 cycles per second (cps) were used and in both cases the same energy (about 2.160 nanowatt seconds) per 1.5 sec-train of electrical pulses remained constant. Antidiuretic substance release from the hypothalamic end of the cut pituitary stalk and from the intact pituitary gland increased during the 36-cps electrical stimulation of amygdala medial nucleus, however the 4-cps electrical stimulation of this structure did not produce any changes in these processes. The results obtained indicate that the medial nucleus of amygdala is able to change the function of the hypothalamo-hypophysial system and can be motivated with high frequency stimulating pulses.