The purpose of this study is to examine the vaginal residence time of certain semen biomarkers.

The study will take approximately 2-3 months to complete. First, you will be screened to see if you are eligible for the study. At this visit the male partner will give a medical history and be asked to donate a semen sample for analysis, while the female will give a medical history, receive a physical exam, pelvic exam, pregnancy test, and will be tested for vaginal infection including Gonorrhea/Chlamydia. If you are eligible (as a couple), you will be called and randomized into one of four study groups. You will be allowed to choose whether you want to take certain samples yourself at home, or have them all taken by a nurse at the clinic. At this point you will either be asked to return home to have sexual intercourse, or the male partner will be asked to donate a semen sample, which will then be inserted into the female's vagina. Depending on which group you are in, you will next be asked to return to the clinic either 4 or 7 times over the next 2 weeks for vaginal swabs.

Once you complete the main study, you will be offered the opportunity to participate in a substudy, where you will repeat the same visits, except that if you chose to have all your samples taken in the clinic for the main study, you will take certain samples at home for the substudy. If you chose to take certain samples at home for the main study, you will have all the samples taken at the clinic for the substudy. Also, you will not need to do another screening visit if you start the substudy within 9 weeks of the end of the main study.

Inclusion Criteria:

• Heterosexual, monogamous couples
• Must not be using birth control other than a tubal ligation
• Must be at least 18 years old, and healthy (if female)
• Must be between 18-55 years old, and healthy (if male)

Exclusion Criteria:

• History of hysterectomy (females)
• History of vasectomy (males)
• Drug or alcohol abuse

Community sample