It has recently been found that sex hormones, like the hormone of the adrenal cortex, have water- and salt-retaining properties. Thus retention of water can be demonstrated both in normal monkeys during the follicular phase of the menstrual cycle [Krohn and Zuckerman, 1937] and in spayed monkeys during periods of experimental oestrogenic stimulation [Guthkelch and Zuckerman, 1937]. In male and female dogs it occurs not only as a result of oestrogenic stimulation but also in consequence of injections of progesterone, testosterone, or pregnandiol [Thorn and Harrop, 1937; Thorn and Engel, 1938; Thorn, Nelson, and Thorn, 1938]. Unlike the rat, in which retention of water affects most organs and tissues [Zuckerman, Palmer, and Bourne, 1939], the water which is retained by some species of monkeys as a result of oestrogenic stimulation appears to be mainly deposited in the sexual skin, and this fact made it possible to devise the following experiments