Abstract
Single injections of guanethidine 15 mg./kg. i.p. did not lower the hypothalamic noradrenaline in cats, but, daily injections of 15 mg./kg. s.c. over a 7 day period consistently produced a decrease in the hypothalamic noradrenaline. Attempts to lower the hypothalamic noradrenaline in rats after single injections or daily injections of guanethidine were unsuccessful.