The effects of prolactin on skin texture, on cutaneous secretion and on molting have been examined in the red-spotted newt under several hormonal conditions. In the adult newt skin is smooth and is covered with varying amounts of cutaneous secretion. Under laboratory conditions the skin ordinarily becomes rough and tuberculated within one or two weeks. Doses of 1.2-120 units of prolactin caused the skin of intact, laboratory-conditioned, red-spotted newts to become smooth and slimy. Similar changes were seen in newts bearing pituitary autografts which are presumed to secrete excessive amounts of prolactin or prolactin-like hormone. No change in skin texture or secretion was detected in hypophysectomized newts treated with prolactin. It has been reported recently that 120 units of prolactin induces molting in the hypophysectomized European crested newt (Vellano et al., '70). Although 3 of 15 hypophysectomized red-spotted newts molted in response to that dose of prolactin, TSH in amounts equivalent to that which may have contaminated the prolactin produced similar results. Thyroidectomized newts showed no cutaneous response to 120 units of prolactin. Thyroidectomized newts kept i n water to which 10 pgm/liter of 1-thyroxine had been added molted only rarely, but when thyroidectomized animals were put into 10 pgm/liter of 1-thyroxine and injected with 12 units of prolactin they began to molt normally and their skins became smooth and slimy. It is concluded that in the red-spotted newt prolactin alone does not induce molting but may facilitate molting, probably through the stimulation of cutaneous secretion, when introduced with thyroid hormone. It is further concluded that although prolactin induces changes in skin texture and in cutaneous secretion, those responses are to some extent mediated by the thyroid hormone.It has long been accepted that the thyroid is the endocrine gland that exercises primary control over molting in the urodeles (Adams and Richards, '29; Adams, Kuder and Richards, '32; Osborn, '36; Jmrgensen and Larsen, '60; Clark and Kaltenbach, '61). Recently, however, it has been reported that prolactin induces molting in hypophysectomized (Vellano et al., '70) and in thyroidectomized and castrated (Vellano, Mazzi and Sacerdote, '70) specimens of the European crested newt (Triturus cristatus carnifex). Although rejected by some workers (Adolph and Collins, '25; Adams and Gierson, '32; Clark and Kaltenbach, '61), the suggestion has been put forth (Schultz, 1889; Dennert, '24; Chadwick, '48), that in J. EXP. ZOOL, 184 36S382 molting, cutaneous secretion accumulates beneath the slough, forcing it from the body. Various findings have given indication that prolactin affects skin texture and cutaneous secretion both in the redspotted newt (Adams, '32; Reinke and Chadwick, '40; Grant and Grant, '58) and in the crested newt (Vellano, Mazzi and Sacerdote, '70).The present study explores the question of whether or not prolactin is capable of stimulating molting in the red-spotted newt (Notophthalmus v...