Hypoactive sexual desire disorder (HSDD) represents a persistent or recurring deficiency or absence of sexual fantasy, thoughts, and/or desire for receptivity for sexual activity that causes personal distress.' A number of factors may contribute to HSDD, including relationship issues, sexual attitudes, emotional and physical health, medication use, as well as low androgen levels. Low androgen levels have been well documented in patients with hypopituitarism, adrenal insufficiency, following administration of glucocorticoids, as a consequence of bilateral oophorectomy, and a result of oral estrogen administration to postmenopausal women. Estrogens increase the production of sex hormone binding globulin (SHBG) by the liver, which in turn binds the majority of the circulating testosterone, thereby, reducing the free or bioavailable fractions of testosterone. Androgens have been used for many decades to treat postmenopausal women with low libido. Several randomized, double-blind, placebo-controlled trials of testosterone therapy have been published. (2-5) These trials have generally demonstrated an increase in libido and sense of well being with testosterone replacement. Most of the trials have used doses of androgen that were supraphysiologic. An exception was the study of Shifren et al., who administered testosterone transdermally in doses that more closely approximated physiological testosterone levels for premenopausal women.(5) In this study of 65 postmenopausal women receiving concomitant oral estrogen therapy, investigators found that a dose of 300 mcg/day of testosterone administered transdermally resulted in an increase in reported frequency of sexual activity and an increase in overall mood and sense of well-being. Additional Phase II studies utilizing testosterone patches demonstrated similar findings. The present report describes two Phase III trials of transdermal testosterone administration in a large number of surgically menopausal women.