- Progesterone microspheres intramuscular injectable suspension 300 mg Study subjects: 48 healthy postmenopausal women, 45 - 60 years. Brief description: After written informed consent, 48 eligible women will receive pretreatment with oral estradiol valerate, then, 14 days later, those with adequate endometrial thickness evaluated through ultrasound will be randomized to study treatments (one IM injection each 7 days, for a total of 7 doses). 10 days after the first progesterone dose, an endometrial biopsy will be obtained. Blood samples will be obtained for pharmacokinetic study.