This study is designed to evaluate the endometrial safety of a testosterone patch as treatment for low libido in naturally postmenopausal women.

Naturally postmenopausal women with hypoactive sexual desire disorder (HSDD) will be randomized into a 52-week, multicenter, double-blind (DB), parallel-group, placebo-controlled study. Patients will be stratified based on whether they use concomitant estrogen/progestin therapy and then randomized in a 4:1 ration to receive either testosterone transdermal system (300 mcg/day) or placebo. Patients using estrogen/progestin at the start of the study should maintain this therapy throughout the study; patients not using estrogen/progestin at the start of the study should not initiate estrogen/progestin therapy throughout the study. Endometrial biopsies and transvaginal ultrasounds will be collected/performed at screening and study exit for all patients. Safety will be assessed by adverse events, reports of vaginal bleeding, lipids, serum chemistry, and hematology. Physical exams, pap smears, and mammograms will be monitored.

Inclusion Criteria:

• Women will be screened for study participation and must be at least one year post menopausal, 45-70 years old, in general good health, and may or may not be on hormone therapy, and must have low sexual desire which causes distress.

Exclusion Criteria:

• Women will be screened for study participation and must not be using androgen therapy or have any medical, physical, psychological, or pharmacological condition that could make participation unsafe or confound the safety evaluation.