The objective of this study is to determine the safety and effectiveness of three doses of asoprisnil, compared to placebo, in the treatment of women with endometriosis.

Endometriosis, the presence of endometrial tissue outside the uterus, is a progressive, estrogen-dependent disease that occurs in menstruating women of reproductive age. Although all major endometriosis therapies are effective for the treatment of pain, no single treatment is superior to others in terms of efficacy. The major drawbacks of the current medical therapies are severe side effects such as hot flushes and osteoporosis. The objective of this study is to determine the safety and efficacy of asoprisnil 5, 10, and 25 mg tablets, compared to placebo, administered daily for 12 weeks to women with endometriosis, by assessing whether asoprisnil administration diminishes the pelvic pain, dysmenorrhea, dyspareunia, excessive bleeding, and analgesic use associated with this disease and lessens the subjects' perceived pain symptoms. Otherwise healthy women with surgically confirmed endometriosis will be enrolled.

Inclusion Criteria:

• Surgically confirmed endometriosis

• History of menstrual cycles between 26 and 32 days

• Otherwise in good health

• Age 18-40 years, inclusive

• Subject had pain graded at Screening and Day 1 according to a scale suggested by Biberoglu and Berhman5 in at least one of the following categories:

  1. moderate or severe pelvic pain not related to menstruation, OR
  2. moderate or severe dysmenorrhea, OR
  3. moderate or severe pelvic tenderness elicited on pelvic examination accompanied by non-menstrual pelvic pain.

• Subject agrees to double barrier method of contraception

Exclusion Criteria:

• Any abnormal lab or procedure result the study-doctor considers important
• History of undiagnosed uterine bleeding or gynecological disorder
• Severe reaction(s) to hormone therapy
• History of osteoporosis or other metabolic bone disease
• Subject currently breast feeding